I would say they should be deleted immediately and with extreme prejudice.
Instead of deleting such questions they should be edited to remove all offensive content so it can be properly answered.
Here's a question which was heavily downvoted initially and the system deleted it even though another user @SwiftPushkar wrote a nice answer citing references:
Why Srimad Bhagavatam Canto 9 Chapter 14 insults women too much?
So one drawback of heavily downvoting and closing prejudicial questions (for which valid answers can be provided) is that some future user will ask the exact question in the same tone and we don't have the original one (with the answer) in the system anymore to close the latter one as a duplicate.
Given that this is primarily a Q & A site, I suggest users focus on answering the central part of question (like @SwiftPushkar did with this) instead of attacking the user in comments or flagging as 'opinion-based', 'abusive', 'offensive', etc.
As a reminder, you shouldn't flag a question as offensive simply because you alone find it offensive:
What makes something rude or abusive and when should I flag it?
Even if a post is a bad post for some reason or another, it is probably not rude or abusive. The rude or abusive flag (formerly known as offensive) is meant to be used only in extreme cases, like hate speech, abuse against people, or abuse of the community or system.
For example, if a user posts obscene images to the site, that should be flagged as rude or abusive. But if someone says something bad about your favorite technology, that probably doesn’t apply.
As a rule of thumb, if you can’t justify something being hate speech or abuse, you shouldn’t mark the post as rude or abusive. Instead, you should downvote the post.
If you don't like a prejudicial question:
Edit it to make it less offensive or less opinion-based.
If you are not up for it, you can simply downvote and move along. Leave answering to other interested users.
By trying to close or delete questions (irrespective of their biased nature), you are also denying other users a chance to write answers (with proper references) and earn reputation.