Well, modern art starts from well before Duchamp or Dada (somehow it makes me think of Harry Potter and Defence Against the Dark Arts), so that's part of it. The whole aspect of modern art is to get out of the academic art drama and therefore, also includes photography and taking in bits of other culture and rise in appreciation of other type of work from other countries. It can be one or both or something else altogether. So when you say you aren't fan of it, you are tossing out a lot of artists from 1850s to 1930s though it's understandable if you don't like some aspects of it like you are pointing at. And Duchamp's work does have a concept attached to it. Using those things available and giving it another concept or idea. He is probably spamming everything he can get away to get more concepts though. It's not like just creating it for the sake of an excuse (the 'even I/my kid/my baby brother,sister could do it' trend which you are giving an example of). Sure, if you want it to mean that way. Either way, modern art is old.
I think it's art if the person who made it says it's art. So yeah, if someone did have a crumpled piece of paper that they created to portray society, then it's art. I may not like it, I may think the artist is a pretentious tosser, but it's still art. I'm pretty sure most 'modern' (I think you're talking about Dada? Which is actually quite old.) artists don't just find/make a random object and attach meaning to it after. Sometimes they don't even have meanings at all, and they are created to be absurd sculptures.