Usually the collective team enforces rules of civility in these games. If someone's being abusive, in most cases, other players will jump on that person to knock it off and just play.
I find that people only start really getting "abusive" (using words like "stupid" or "dumb" to describe the other player's towers) if the person the comments are directed to has been asked politely to remove/upgrade/etc them, but has ignored or refused the request and has offered no explanation for the weird tower placement (such as reserving areas for leech, etc.) So I don't really see this as a real problem.
I find that people only start really getting "abusive" (using words like "stupid" or "dumb" to describe the other player's towers) if the person the comments are directed to has been asked politely to remove/upgrade/etc them, but has ignored or refused the request and has offered no explanation for the weird tower placement (such as reserving areas for leech, etc.) So I don't really see this as a real problem.