Removing issues of illegality from this discussion, who among us has the right to apply "acceptable" to anything other than their own behaviour?
Not all human behaviour falls under Grey as most liberals like to think. I do believe that in some cases violence,murder, rape,stealing, lying and cheating may all be acceptable that's where judgment comes into play, but in most cases they're just plain nasty.Some actions through general consensus are morally unacceptable to society at large through which law's are created.Cheating against one's spouse/partner may not be illegal but certainly is generally thought as morally wrong.
Its human behaviour to put labels to people who do certain actions. We have people who do good called saints, angels... cant really think of many good labels... in the same way we have names to describe those that do evil ie. murderer,rapist, liar, slut...
Labeling may not be a good thing to do, pretty biased really and quite judgmental... but its just what most people do.. however wrong labeling may be, it still doesn't make being a slut right..