Hard science fiction I agree with you. However, I don't think Star Trek has ever pretended to be that
even with the semi-scientific trappings it has at times.
Personally, though, I look at science fiction, along with a number of other genres, as merely a subgenre of speculative fiction. It comes in many different flavors according to taste, but I don't see any opposition
amongst them. At least, I don't see the reason
for any such opposition though some act as though it's there.