Well, stereotypes are almost all to some degree based in reality, the problem is when they are used to generalize about a population. The stereotype that hip hop and related genres are nothing but guns and bitches is first of all: a stereotype. It's perpetuated by artists who do rhyme about such themes and any media that sensationalize those artists. That doesn't make the stereotype valid though.
A Lethal B rap about using guns does perpetuate the stereotype that grime is all about guns and violence. A hip hop video of a song about drugs perpetuates the stereotype is all about drug culture. Neither of these makes the stereotype that all hip hop (grime) is about guns and violence valid. Beyond this fact, to assume then that hip hop that is about only that is just an acceptance of that lazy stereotype about the genre. Then making a questionable moral and "creativity" based claim about the genre being bad based on that very stereotype is both a boring and unnuanced perspective of how slack functions in the context of the music/culture/whatever itself as well as an ignorant perspective of the diversity found in the genre itself.
Obviously people do this to other genres (indie is sad quirky white middle class people), but because of the racial and class divides I referred to earlier the question of "racism" can't help but become more palpable as part of the discussion. Also hip hop related musics tend to be scapegoated more than any other type of music (with the exception of metal) for all sorts of problems in the world. This isn't to say that you're racist, but that statements about urban music in this context are hard to make race neutral.
So in summary:
1) hip hop (grime etc) is not always slack
2) hip hop is sometimes slack, especially what tends to be seen on mtv and heard on your average hip hop radio station
3) slack is not necessarily morally "bad", but it's obvious worthy of analysis.
4) slack is not necessarily "bad" creativity wise either, as mentioned by 28 gun, but can be good or bad depending on quality of the artists' writing, rhyming, and backing beats - just like any other genre. ("Another bossa nova song about 'saudade,' how insightful!" "How boring, another old black man is singing about having the blues!")