They aren't a matter of opinion though, there are defining characteristics accepted by a historied scholarly community that correspond with these words. There are ranges of perspectives as is common in any social science, so it is viewed as a 'softer' science compared to physics or chemistry but it is a science no less.

It may be common for criticial leftists to use these sort of terms flippantly, but that doesn't remove their meaning or usefulness in the larger discourse.