First, I think that people aren't becoming less uncivil but that environments are getting worse. If anything (although this is probably an artifact of increasing age and status) people seem to be getting better, on the whole: fewer mean jokes and exclusionary behaviors. Work environments, with the open-plan trend, are getting a lot worse and more stressful. It used to be that an off-color joke was heard by 2 people in a private office; now it's heard by 40 in a bullpen. Open-plan offices tend to magnify the cumulative effects of microaggressions, which is one of the reasons why every population except for the most constitutionally insensitive one (those who've never had negative experiences, either due to general inexperience or a combination of privilege and luck) hates them.
Second, when you're aggressive or even uncivil, it hurts you with that person. That said, it can be beneficial-- in very small doses. Punching down is bad, while punching up is risky (the best target is a person of high status, that is "punching up", and low character, but with no real power) and if you're perceived as being uncivil for personal benefit, you're just considered an asshole. Usually, uncivil behavior is to one's benefit when (and pretty much only when) one is perceived as being that way for the group: you're a protector. People tire of selfish rule-breakers and firebrands, but those who behave in such ways for group benefit tend to inspire loyalty.
Don't get me wrong: it's generally best not to be uncivil or arrogant at all. It's just not intellectually honest to say that it's always socially detrimental to be that way. You have to be extremely selective in your targets to make it work, though.