Actually screw tape was not rude or obnoxious in that post. He presented a reasoned factual case and refrained from name calling, sarcasm ...
I am not saying you cant present a case to a believer. You should just refrain from things like calling them stupid. Calling someone names breaks down communication AFAIAC.
One of the problems is, you get a particular type of mind engaged, and they react in a wrong-headed fashion. Perfect example was my calling JB out on an Appeal to Ignorance fallacy, and she took it as me labeling her with the epithet "ignorant." Well, *sssssoooort* of...but not really. We spent a good page + trying to explain the fallacy and she pretty much ignored it, preferring to think I/we were insulting her rather than taking apart her argument.
When folks tie their identities to their arguments, they cannot differentiate between someone saying "that idea is stupid" and "you're stupid." To them, they're synonymous.