Many first unpopular opinion, which seems to be not unpopular anymore was in 7th grade (approximately 13-14 years old) we had a project week about drugs. I was the only one who said that I actually thought drugs should be legal. That was 20 years ago.
Other than that the closest thing to an unpopular opinion is that I sort of think arranged marriage between people in, e.g. the west and Thailand is ok IF the marriage also include empowerment clauses, e.g. full support for the woman to study or whatever she values. Also, there should be some beneficial exit clauses. It is sad that the women find these arrangement/arrange marriage beneficial, but as long as they do I support their desperate attempt to better their life. And yes I do know of some examples - both very good and bad.