I can understand that, sometimes people just want a catchy songs, but some of the stuff coming out is borderline retarded.
Except that one punchline doesn't make a whole song, you should be talking about the lyricism in the song as a whole. One line may not make you think, but an entire song that contains lyrics that expand on some kind of subject matter with a some level of depth, creativity and cohesivness will sure be mindblowing.
This couldn't be further from the truth.
For starters, Rap music, unlike other genres of music, (whose most notable characteristics are either talented voclalists with powerful voices and or talented musicians that can play instruments), apart from having talented producers that make beats, HEAVILY depends on lyricism. It's essentially poetry spoken over a beat.
Rap is more about how well you say something, rather than what you say. That's why good rappers try to use metaphors and similies to get their points across and whatnot.
So therefore, breaking down rap lines is pretty much inherent to enjoying a rap song. Because you can basically go "Ohhh damn, just look at how he said that! That's pretty clever lol". That's the nature of the artform. The MC tries to be clever with what he says, and fans enjoy the beat and flow and delivery, along with the level of lyricism and creativity displayed.
Not to mention that, people can bump a song (And enjoy it) and look up the lyrics later for clarity.
You're sound like someone that just listens to rap just for the beat (Not saying that you're dumb or a sheep or anything), what about what the MC is saying and how they say it? Isn't the quality of poetry (Which what rap essentially is) judged in this manner?
Now I'm not saying that you can't enjoy a club anthem or anything, I'm just saying that you can't knock breaking down/analysing lyrics, because it's something that is natural when it comes to listening to rap, maybe even more necessary now than ever.
This isn't really mutually exclusive, regular people do criticise stuff.