One thing about Maki is that she believed that Sakura and Machida were doing the dirty, so she didn't blackmail anybody, she just shouted her suspicions during a meeting between interested parties, I don't see how that is so evil, she kept it bottled up until now. As for the compensated dating, I would ask anyone who believes they would have known better at the same age and the same situation, to throw the first stone. She probably honestly believed it was no big deal to fuck a scumbag for money.
That's also why I think the friends didn't think it was that much of a deal for her to have done those things. She just felt like they had put her aside and felt rejected.
That's my take on it.