That’s because most people think things like using ad hominem attacks to discredit people is the same as making an actual argument.
But it’ll get you lots of upvotes!
Sad part is, I’m fine with unions, but, as with everything else, they aren’t some one size fits all solution. Statements like people who don’t like unions hate fairness or that all people at one company would disagree that unions aren’t the only solution aren’t arguments. They are cherry picking and straw man statements treated as obvious facts. They sound good, but are completely without actual substance. People who rabidly support unions this way don’t help their cause. No one who disagrees with them will actually change their mind.