What do you think about not giving credit, ignoring laws/licensing and passing off others' work as your own?
Do you not remember how Gen X were called "slackers" by their elders?
Or how the hippies of the 1960s were also chastised for their lack of industriousness, misreading "Turn on, tune in, drop out" as "get stoned and do nothing."
Or how the term "Lost Generation" from the 1920s comes from Gertrude Stein's account "When a young mechanic failed to repair [her] car quickly enough, the garage owner shouted at the young man, "You are all a "génération perdue."" (https://en.wikipedia.org/wiki/Lost_Generation ).
Instead, see "laziness" as the perpetual but tired smear by old people irritated about the young.
To give some specific examples to back me up, this topic of plagiarism is not new to the 2000s. Some quotes; first from Tom Lehrer's song "Lobachevsky" from the early 1950s: "I am never forget the day I first meet the great Lobachevsky. In one word he told me secret of success in mathematics. Plagiarize!" and second from T. S. Elliot in 1920, "Immature poets imitate; mature poets steal" (https://quoteinvestigator.com/2013/03/06/artists-steal/ ).
What is new about the current generation is the oppressive use of legal and emotional means to interpret all forms of copying as illegal and immoral.
Legal means includes DVD encryption, along with prohibitions on publishing copy protection circumvention code. This form of encryption often prevents or hinders legal uses of material under copyright protection, like adaptations for the blind.
As examples of "emotional means", think of the "don't copy that floppy" ad campaign of the 1990s and use of the phrases "steal" and "pirate" with their connotations to criminal law instead of "infringe" and its use in civil law.
Copyright law has become more strict, with more and more things covered under copyright. Before the 1970s, with rare exceptions, it was perfectly legal to copy software. (See Gate's infamous "Open Letter to Hobbyists", during the time when US law was changing to say that software was under copyright law.)
See also the sampling in hip-hop music, which after Grand Upright Music, Ltd v. Warner Bros. Records Inc became prohibitively expensive.
My point here is that the most recent generation is more likely to have a sense for what is right and wrong in copying based on the economic desires of large companies. Practices which are now illegal were once legal and commonplace in the not-too-distant past. Your own text highlights one of those changes - until the 1970s, copyright had to be asserted explicitly.
Lastly, "plagiarism" and "copyright" are distinct things. Unlike copyright, plagiarism is not a legal concept. I can plagiarize something which is in the public domain. I can infringe on someone's copyright without plagiarizing.
All that said, to answer your question - "it depends." There's the old joke that all C programs are derived from "hello world" in K&R. I have a blog with code examples. I don't care if anyone uses them, even without attribution.
Many books have been written about the topic, so without details it's too generic to answer here, other than to point out that there's a lot to unpack in your question that you might not be aware of, given how you worded the question.