Eh, I don't think it's that big of a deal. We have plenty of comedy based on serious topics, in manga and other media - that doesn't make them any less serious or important.
Personally, I'd be more worried about a concentrated push of topics/narrative made by corporations or governments than one relatively unknown manga.
Let's not get crazy and treat everything seriously all the time. Hell, sometimes it feels like people who've been through really bad stuff are more willing to laugh about it than those who didn't. Respect and thoughtfulness are important, yes, but so is humor - humans can find it in the worst of times, that's our strength.
As for manga itself, it's funny enough. Not really my type of thing long term but I didn't really find anything wrong with it. Never been to a prison though.