Crowds have the right to react, cheer, boo and chant as they please. Doesn't mean they should do it. Crowds aren't booing Reigns because of the way he's been booked, more-so because it's a trend. Casual fans who have no idea of the internal workings are booing him, for booing sakes. Not to mention, that the marks that do boo and sing Cena's song are just adding fuel to the fire. They're pushing them as "polarizing" and people that can garner a reaction out of anyone; if people really wanted to get these guys out of the top book, they'd stop reacting because obviously booing doesn't do anything in Vince McMahon's eyes. And to that note, they think any match with 2 near falls that goes over the 8 minute mark is warranted by "This is Awesome!" and a table spot gets a "Holy Shit!" chant. I've seen far better matches in ECW, and they hardly chant those unless it was really crazy.
Another thing is that they ruin the show. The crowds spend more time putting themselves over than actually watching the show. You have people who buy first row tickets to dress up and try to become memes. They think they're hot shit and start chanting smarky chants like "We are awesome!" which is just cringey. They divert the attention of the show, and the wrestlers getting pissed off and with good reason. The first time it happened after WrestleMania 29, it was cool. Since then it's just been about who can be the best Mania crowd instead of having fun. It's stupid, ruins the show, disrespects the wrestlers, annoys viewers and attendees alike.