Japan is a little different than America is with regards to animation; they see it more as another medium to present a story or a vision than America does, where anything animated is predominantly thought of as 'kiddy', i.e. 'cartoon = for kids'. The particular term would be the Animation Age Ghetto, and it's a shame that its influence is still so strong.
You may say that shows like My Little Pony are childish. Fair enough; the studio intended the audience to be the 5-11 girl demographic (albeit with plenty of Parental Bonuses like the old Looney Tunes to make it enjoyable to watch for older people, since that was one of the intended goals of the show's creator). You may say that shows like Family Guy and its ilk are childish. Fair enough; those kind of shows are filled to the brim with vulgar and immature humor that does not strike one as 'adult', in the sense of thematic complexity. But going about animation in that way is VERY limiting; if live-action shows had to follow the standard that you seem to place on animation, then everything would either be G and PG ("It must be for kids!") or NC-17 ("Trashy junk filled to the brim with shock humor!").
I don't think you'd describe Princess Mononoke as childish. Or Watership Down. Or Neon Genesis Evangelion. Or Grave of the Fireflies. Or Paranoia Agent. Or Cowboy Bebop. And so on and so forth.
Animation != Childish
Never heard of any of the stuff you are describing and not interested.
You can describe liver and onions in any fashion you desire and I am not going to eat it. Same as the little girl cartoons and dressing up like a pony.
Simply not going to change my mind about it being weird and certainly not mainstream or normal.