At what percentage would it be justified in to change the law, and not make it illegal anymore?
That presumes people are consistent in what they do, what they think others should do and what's really right. Take for example speeding, very few want to do away with speed limits entirely. Most people break the speed limit themselves. In fact, almost every year around school starting they have speed traps and some of those caught are bringing their kids to school. Like, everybody else should drive slow but I was in a hurry so... hypocrisy at its finest.
I think most people fundamentally think the creator should be compensated in some way. You read a book, the author deserves something for writing it. That doesn't mean the public find any particular offer satisfying, maybe they think it's too inconvenient. Too expensive. Too limited to a particular format or playback device or online connectivity or whatever. Or that you don't have money to spend but it's an IOU for later. They don't want to see people crucified for minor infractions. They don't want restrictions as legal customers. They don't want to support a surveillance state.
The pirate party tried, it did get a bit of traction when it was the subject of a massive government crackdown. Like if you're going to come down on it this heavy handed, we'll get rid of it. So they backed down and made it one of those marginally illegal things, how many of those young men have been caught? What kind of punishment did they get? I think the answer to that is almost nobody and a fine at most. So I think most are fairly okay with that stalemate, like speeding. Most people do it, few get caught but if you do pay the fine and move on. Even if the speeders are a majority, they won't legalize speeding.