Instead of thanking someone, you could compliment them, or at least comment on how uncommonly reasonable they are. Someone once wrote this in response to me saying I was wrong:

... You know, I think we may be having a polite discussion, informed by reasonable data and fact-checking, and with considered re-consideration of claims and opinions, ON TEH INTERWEBS!!! ... I'm a little weirded out by this.

I didn't find it patronizing; I liked the implied compliment that I was unusually polite and reasonable.