Colorful and sometimes forceful means of expression? Sure, it can be used like that, but in my experience, I could NEVER have a serious conversation with people who curse excessively, and historically, its been used as a way to insult others intentionally or it was a reaction to violent emotional outbursts.
We may not be Vulcans, but that doesn't mean Humans can't achieve that kind of high emotional control if they chose to do so.
However, I wasn't referring to Vulcan level of control... just control to allow oneself to remain highly objective in emotionally charged situations and not let emotions in they way (a lack of which is causing massive problems for us in real life).
Look at "This Side of Paradise." Kirk and Co. actually find it weird that the brainwashed colonists never lose their cool, and are relieved when, after after the spores are burned out, the settlers go back to bickering and quarreling among themselves, like normal humans do. I'm suddenly imagining an updated version in which Kirk finds it weird that the colonists never swear -- and breathes a sigh of relief when they start cussing him out at the end.
There is a difference between forced brainwashing and teaching people to have a better grip on their emotions so they can retain their cool in charged situations to think objectively.
Of course they would return to bickering, because the writers never thought to implement the idea that these people would probably NOT bicker to such an extent (or at all) in such a future to begin with.
Remember that environment is what shapes behavior... behavior doesn't arise from vacuum.
The way I see it, any "utopian" society in which people seem to have "evolved" beyond profanity is probably more like a sterile dystopia created by brain-warping spores or an insane computer-god.
See also "Return of the Archons," "The Apple," etc. Wanna bet that Landru doesn't approve of swearing?
There is nothing 'utopian' about it. People always jump to this conclusion without understanding that it implies 'perfection' which cannot exist in reality.
All you can do is achieve something FAR better than what we have now... and just because a society doesn't use profanity or it managed to solve poverty and eradicate wars, it doesn't mean its sterile or boring by any means - you don't live in such a society so you don't know the full extent of what living in such a society would mean.
You only THINK its sterile because you were taught to equate profanity with being 'colorful' (much like various people today think that you need to get drunk in order to have a good time - whereas we know that's not the case - and when you think about it, alcohol is responsible for a LOT of issues in developed nations).
And Trek writers have been and continue making same mistakes as you do.
I personally wouldn't prevent people from using profanity... I'm just saying that they don't have to use it to be colorful, or interesting (or to make life worth living).
At one point people also thought that smoking is 'colorful' and makes people interesting or cool (heck, they went so far to see it as healthy).. and as a civilization (though we are FAR from civilized), we actually banned it from indoors and discovered its bad for our health. Sure, that doesn't stop some people from smoking, but there's far less people today who do smoke (and eventually, we will probably reach a point where no human will actually smoke - or drink alcohol for that matter - will that make us 'sterile'? Far from it... it will simply change the dynamic of how society as a whole behaves and it will still be interesting and colorful... in fact we could argue that there are ways to be colorful and interesting without doing 90% of the stuff we do right now - but its difficult for many to imagine).
