Why? Why does it bother you what a complete stranger decides to call themselves on their switch account?
Why not mind your own damn business.
It bothers me because when you connect to my system to play a game, we're sharing a play space. Your're on my team, or your my opponent. Your name is displayed is in my home. It's disrespectful to be doing that kind of shit.
Second, Nintendo is really open as far naming (small blocklist and you can change your online nickname anytime without limits) and messaging (i.e. MiiVerse, Inkopolis etc.) goes and I think community self-regulating is important to mainting that level of freedom.
I'll make the full case in an analogy. If I overheard people saying "fag" or "nigger" in a familar conversation, I wouldn't interject and tell them what they can and can't say or think. If it's not disruptive, I agree; it's none of my damn business.
But if we were in a shared space together - say a pick up basketball game or a bar trivia night - trust and believe I'm gonna tell them to knock that shit off if they want to play.
Now I don't have those analagous tools to talk on NSO, So, I reported and blocked 'IKillFags' (real example) for an 'Inappropriate Nickname', as I've tagged explicitly sexual messages in Inkopolis.
Maybe it has to do with being a Nintendo platform too. I've never reported anyone on PSN for anything other than blatant cheating or griefing, and the games where people are shitty on voicechat, I can say "hey, knock it off" and it's usually sorted. Not only are those avenues not there on NSO, but I can't help but imagine much younger people with much different expectations going into Splatoon than say a 10 year old playing Call Of Duty. Again, you might be more compelled to check someone saying some raunchy shit you'd overhear at a nightclub if they were saying it in a Chuck E. Cheese.
Hope that explains how and why it bothers me, and why I think it's my business.