Heels are there to be booed. They want you to hate their guts. If you liked Punk more as a face than a heel, then he's doing his job. If you hate a heel, you want a face to beat him, thus you cheer the face more, buy his merchandise, buy PPVs where the two are facing off, and the face becomes a big star. Heels are star-makers.
What do people hate?
1) Cowards and Cheaters
2) Arrogance
3) Being told they're scum.
Heels have to cheat and run and hide so that the face seems all the more heroic and people boo the heel all the louder. Angle was the lone exception, he was allowed to beat people just because he was better, but even then, he was only allowed to turn it on for big PPVs.
Wrestling plays upon the most basic of human values to tell very old stories. While you shouldn't use it as your sole moral guidance, fundamentally good morals are communicated in the WWE. Faces preach being honourable and courageous and standing up for yourself, so heels have to do the opposite so that when they lose the status quo is upheld.
Punk is booked as a very traditional wrestler. He has very solid fundamentals but his greatest skill has ALWAYS been being resourceful. He doesn't dominate or dissect, he normally find a way to win after trying a little of everything. He's made a career of it. That's why his moveset is so limited and simple. He does things that make sense and nothing more.
They aren't saying that drinking and doing drugs is good, they're saying that someone telling you what to do is bad. Triple H highlighted that it's about freedom of choice. Matt Striker puts over that it's not the message, it's the messenger. Punk lords it over people and they don't like it.
Mission accomplished.
End of the day, he gets booed, a LOT. When he was a face, I don't recall him getting monster cheers. Whoever suggested Vince turned him because he was getting too big must have been watching the wrong product, because he was getting very little reaction after he won his first world title. Now he plays a fantastic villain.
Plus, I'll repeat my point, being a heel got him signed.