As a parent of both a teenager and a kindergartner, I have a responsibility to protect my children from certain types of language/violence. I've let my teenager see certain R rated movies of which I approve (the first being Run Lola Run, because she enjoyed movies as a whole, and I so thoroughly enjoyed it, I hoped to teach her some of what little I know about cinema). However, on the whole, my attitude is there are things that are appropriate for children, and things that are not. "Adult" entertainment is not. That does not mean adults should not see it. (I know, the definition of "adult" entertainment, at least as it pertains to television, is changing - that's where the individual decision comes in to play.)
To get back to the point of your question, I'd be concerned if someone shouted obscenities in public, if for no other reason than I would consider that person to be irrational, and possibly dangerous (not necessarily a terrorist, or a suicide bomber, but perhaps just nuts enough to throw a punch if I looked at him/her wrong).
If someone is expressing their opinion publicly, I say they have the right. But not necessarily to disturb the peace or incite a riot. The level of shouting in that case disturbs me more than what is being said.
Nigel