“Thank you for seriously engaging with my beliefs” is something that makes sense much more broadly.
I do think that there is something low-status in the phrasing. “Thank you for taking my beliefs seriously enough to criticize” I would call creepy. I suspect that there is a better way to phrase this. “Thank you for the debate” is a perfectly ordinary statement, but probably not adequate for this situation.
“Thank you for presenting strong arguments against a belief that is important to me!” is something that only makes sense on LessWrong. :)
“Thank you for seriously engaging with my beliefs” is something that makes sense much more broadly.
I do think that there is something low-status in the phrasing. “Thank you for taking my beliefs seriously enough to criticize” I would call creepy. I suspect that there is a better way to phrase this. “Thank you for the debate” is a perfectly ordinary statement, but probably not adequate for this situation.