Confusion over "respected" in the following sentence

Solution 1:

It means that many people consider X the opposite of respected.

Not a few means "many".

An oxymoron is a witty combination of opposite terms.

And, yes, this sentence is very convoluted; that is probably done ironically and on purpose. It is a figure of speech that is supposed to be mildly entertaining.

Solution 2:

I think it may also intended to convey that the author of the sentence may not agree with the statement. Maybe more than 'not a few' consider it, as in, 'many', but the author considers those 'many' to be incorrect in their usage so therefore they highlight this disagreement with the use of 'not a few'.

You could also have the complete opposite interpretation. I.e., they agree with the 'not a few' and are trying to use hyperbole. I.e., "not a few people consider wife-beating to be wrong."

It really depends on the context of use which is really hard to determine with what is provided.