2) Being a citizen doesn't just have benefits but also responsibilities. This is why we pledge allegiance.
At age 21 I had to register for the civil service. That means that if my country goes to war and I'm drafted then I must fight and possibly die for my country.
An illegal immigrant will not be drafted.
It also means other things I'm bound under federal law like paying taxes. There are also other civil duties like being on a jury to judge my fellow citizens. As a citizen, I'm bound by the laws on our constitution and those created by our legislature.
3) The privileges of a citizen allow them to contribute to the way our democracy functions including the right to vote.
An illegal immigrant cannot vote.
The rest of my argument was already stated above to you. If we completely open the borders to everyone, then our government wouldn't even be able to serve the current legal citizens.
You may dislike the system but in other countries such as Japan and Germany it is even more difficult and exclusionary. They are based on parentage and while that make more sense to you, it actually ends up leaving large classes of immigrants unnaturalized.