The person sharing their unpopular opinion is doing exactly what’s expected of them, so why downvote it when you agree that’s it’s an unpopular opinion? An upvote would be you agreeing that it’s an unpopular opinion. Downvoting it means you’re either an A-hole or you disagree that it’s an unpopular opinion.
Now I leave you with a joke. Silver was walking down the street and bumped into gold. Silver says "Ey, You’. Gold replies “Ey, G!”
If a person thinks more people should see an unpopular opinion, they snould upvote it. Theres no karma here. The function of up and down vote is promotion or relegation.
An upvote means that the content should be shared, a downvote means it should not.