A very interesting point of view. I agree somewhat. I have read a few books where the characters seem to swear just to create a more 'adult' setting. 'Ooo. Look at me. I say f--k a lot. I'm an edgy adult story.'
Personally, I find cursing immature actually. Don't get me wrong, insert an expletive at the right moment with the right person (like sweet grandma through the whole story suddenly lets loose with one), or a normally reserved or controlled person cutting loose, might very well set the tone VERY appropriately.
To me it shows one of two things. Either a lack of control/extreme of emotion, or a lack of an education (and by that I mean, having learned better ways to express yourself). It is doubtful that most teens
now-a-days, have not heard any word you can come up with. Those days of innocent/ignorant children are unfortunately long past. Now that doesn't mean that all restrictions are off because of that, and they're still easily influenced (mostly as to what is "cool"), however, it's not a deal breaker like it used to be, where the kid will go running through the house shouting some new word, or will insure their life path will degenerate into one of sin.
That said, there is a place in literature (good or bad up to you to decide) wherein expletives are not only appropriate, but in my opinion, mandatory.
You can write about X person who grows up under Y terrible circumstances in Z backwater slums, yet the second they open their mouth speaking like some seminary school scholar, well, that shoe just don't fit.
In what I'm working on now, the protagonist comes from VERY-low beginnings, and her life simply just kept slipping lower. She has virtually no anger control, is uneducated, and has never had any guidance except by the worst sorts. On the same token, the vast majority of the population now lives in slums speaking a pidgin made up of many languages mashed together.
If you're familiar with pidgin and slang, well guess what makes up a good chunk of it? Even refined slang like that from the south. Fudge=f***, sugar=s***, crud=cr*p/s***, darn it=d*** it, etc.. Pidgin works the same way (real world). Cutesy or hip words are used in place of common curse words... 'to mean the exact same thing!' But, because it is now slang or pidgin, though meaning the exact same thing and everyone knowing it, they feel it does not.
The reason is, it shows restraint and control. The same innocuous word can be used in both extremes however, and suddenly it has two very different extremes of meaning/intent, based on context.
SO as much as it may not be appropriate for young readers... meaning as far as I'm concerned, should not be read by them, to not make that leap where appropriate is... inappropriate
Everything has its place. It's just that, that place isn't for everyone.
K2