It's called Old because there's a New Testament, which overrides the Old where applicable. And Jesus was a peace-loving man.
Firstly, Judaism is not the Old Testament at all. Christian and Jewish philosophy, and for that matter Muslim philosophy are all very different. As such, there are different interpretations of the same input data one could say. The problem is not even the input data is the same. (btw: the term Judaeo-Christian suggesting commonalities IMO is wrong and might as well not exist because it's lumping mostly different things together).
The Old Testament is a Christian edited version of various selections of Torah, namely 5 books, but even the divisions differ between Judaism, Catholicism, and Protestants. Beyond potentially reorganizing and excluding content, another disconnect is that the Torah according to most Jewish traditions is both a written and oral tradition. Most Jews who are knowledgable about theology would agree that Judaism is not explained, nor summed up, or even represented by the Old Testament, let alone the Torah itself. Further, oral traditions as well as cultural and religious duality are so important, that you can't actually read things like the Torah without knowing them. Philosophically, there's a pretty large difference between Judaism and Christianity on so many levels related to spiritual significance and directions of text.
Even inside Judaism there are huge divisions. Note that there are people who devote their lives to studying Torah and while I have a few interesting things to say about that (depending on the context, not nice things), I acknowledge it as intellectually interesting in that you have many people with different interpretations, including seeing the text itself as liquid or even adaptable (ex: to modern times). This kind of studying, questioning, and analysis is encouraged in Judaism. While it happens as well in modern Christianity, the views and treatment of text here are very different suffice to say without going into great detail.
Another large issue is translation. Ancient Hebrew is just that, ancient and not completely understood with 100% accuracy even among native modern Hebrew speakers and scholars. Even Aramaic and other languages of related texts have changed. Pronoun translation alone from a gendered language like Hebrew to English is bad enough for example, but factor in that often the path could be as muddled as Ancient Hebrew -> Greek -> Latin -> <Your Language, ex: English>. There are of course more modern direct attempts, but quite often translations are not from the source, but rather translations of translations. Between translation, time, and oral traditions, there's a lot of signal decay.
As for other things about Judaism related to the Old Testament, the mention of it being 2.0 splits a lot here. Judaism has all kinds of commentary, supplementary texts, additional scrolls, and other books that are various degrees of "holy" or even "canon." Pretty much none of these exist in Christianity and only a few play any role or influence on the New Testament (aside: New Testament also morphed over time and had translation issues and so on). To make matters more interesting, some interpretations become part of oral law and even influence the readings themselves. Indeed, words are often changed or substituted by some people, while others would rather die than do anything but what they perceive as read things in their original form. If you purchase a book even that contains the Torah and what the Old Testament is based on, each version will have wildly different commentary, and sometimes even omissions.
I could go on, but since it's HN, let me just summarize a few things about the Old Testament in computer terms to get back to the point:
- Christianity vs. Judaism is not like a Git branch, but rather taking a few conceptual things and writing different implementations. There is little if any shared code, but maybe you could think of it as people who worked on an old project together and then had a split and built new things.
- New Testament is not v 2.0 but more of a re-implementation with what could argue is some code refactoring and slapping on a new interface (some things in common at a high level, but not at a lower level). Some (a lot) features are missing in the re-implementation.
- New Testament is heavy on marketing Jesus and his disciples, while ironically this would be an offense punishable by death by Old Testament and the Torah (you are not allowed to call yourself or be called the Messiah, the conditions for the Messiah are specifically laid out and according to these texts have not happened). New Testament would fail build tests and constraint checks.
- Christianity and Judaism have different licenses, plug-ins, benevolent overlords, and so on...
- The human compiler pretty much is broken because people aren't following the source of either most of the time, probably thankfully. I know the goats, sheep, etc. are probably happy aboutr that, let alone humans.
Well I am sure someone is going to hate me now or kill me for sacrilege. For the record, I the only thing I believe in is the electric guitar. I just grew up around religious people and spent some time studying it to understand what it was I didn't like.
The Old Testament remains part of the Christian canon and continues to be revered as scripture by all Christian sects that I know of. Dismissing it as "Jesus undid all of it" is disingenuous.
The Quran and the Bible cover a great deal of the same material. Christ is a major figure in the Quran as well and is known as Isa. The principles taught by this character and the narratives surrounding him remain very similar in both accounts.
Islam is not an existential threat to the United States or the Christian world. We know this because we had peaceful relations across the Muslim world until the mid-late 1970s, 200 years into the United States's existence.
It's certainly possible that some people insist their interpretation of Islamic works mandates that they kill all non-Muslims. Similar interpretations could be made of Christian scriptures (and indeed, the Book of Joshua thoroughly documents many occasions when Israel raided cities, including occasions wherein they were instructed to kill any living person -- man, woman, or child -- that inhabited it). Nothing Jesus taught would preclude such actions by Christians today. Jesus even said that he came not to send peace, but a sword.
The important thing here is not to pretend a) that Christians are fundamentally invulnerable to the same interpretations or impulses, because we know from history that they are not; and b) that Islam is an existential threat in total based on the malicious practices or interpretations of some of its prominent sects, because we also know from history that it is not.
To the extent that it exists, the Muslim world's conflict with the West is based not on intractable doctrinal conflicts, but social and political changes that occurred in both regions/cultures over the course of the 20th century. Here's a few:
* The importance of petroleum to the West caused us to become very sensitive to the existing political powers in the Middle East
* We deposed a not-entirely-hostile democratically-elected head of state and set up a puppet government in Iran to protect our petroleum interests, which was overthrown by religious extremists.
* Muslims felt threatened by the creation of Israel
* Muslims observed the sexual revolution in the United States and really did not want that to come and disrupt their traditions
* The Sauds used the power they accumulated after the fall of the Ottoman Empire to promote a restrictive interpretation of Islam that served to entrench their dynastic monarchy, unifying religious and political authority, as is typical in dictatorships
... and so on. There's actually a lot of interesting political events that have gone into the current climate. It can't be boiled down to the simplistic and obviously false conclusion that "Islam and Christianity can't co-exist", as a) they're derived from the same traditions, such that their holy books recount many of the same narratives with only minor variations; and b) they've successfully co-existed for 1400 years, the overwhelming majority of which were not spent in conflict, and many of which were spent in cooperation and trade.
Please do not fall victim to the people trying to bait people of differing religious backgrounds against each other. That is not how peace is achieved. We need to understand each other, not belittle the others' traditions.