Sometimes such questions are good and useful
Sometimes such questions are useful (so a blanket ban might go too far).
A "comparison" question might be useful, for understanding (specifically) Buddhism; for example:
OTOH (looking at other christianity-tagged topics) I see less purpose in Is Jesus considered to be a buddha? You could consider closing that, on the basis that it breaks this rule:
You should only ask practical, answerable questions based on actual problems that you face. Chatty, open-ended questions diminish the usefulness of our site and push other questions off the front page.
We are already able to close bad questions
We can close questions which are:
- Too subjective
- Off-topic (if they're more about another religion than about Buddhism)
I see that people have already, rightly, closed some questions for these reasons.
Sometimes you might want to close a question temporarily, demand that it be improved (or edit it yourself) before allowing it.
Moderators can moderate answers too
Moderators can "protect" questions.
The main objection in the OP seems to be that this type of question tends to attracts bad answers, which leads to arguments. So perhaps you could achieve your objective by extra-strict policing of the answers:
Deleting answers which you consider off-topic: e.g. if you allowed some-or-other question because it's 75% about Buddhism and 25% about Christianity, feel free to delete any answer that's 25% about Buddhism and 75% about Christianity.
Extra-strict editing of answers by all moderators, to ensure answers are not controversial (including removing any parts of an answer that are "a bit tongue in cheek").
Deleting answers, and non-trivial editing of answers can really only/mostly be done by moderators.
Also note that just as a moderator can close a question until the author has improved the question, moderators can also delete (i.e. hide) any really problematic answer until the author has improved the answer (the author can still view and edit their answer while it's deleted, and then flag it for reopening).
And moderators can moderate comments
On some sites, moderators are strict about whether comments are on-topic.
- Comments are only meant to be for suggesting improvements to (or criticizing) an answer
- Other comments are off-topic:
comments aren't intended for dialog, and
off-topic comments are deleted
- Existing comments can be sent/converted to a chat room