It wasn't Snape's choice to humiliate Hermione publicly — that was Dumbledore's decision, making use of Snape's "evil potions master" persona. Note that none of the other professors speak up, except for Quirrell, who is a temporary hire and need not follow Dumbledore's direction. Minerva doesn't even show up, presumably so that she doesn't have to sit and keep her mouth shut.

Dumbledore explains to Harry in chapter 77 that Hermione had to be seen to lose publicly in order to de-escalate the conflict with Slytherin. Dumbledore doesn't actually know that Snape was involved in escalating the conflict.

I'm still not sure why Snape wanted to escalate conflict between the bullies and SPHEW, but regardless, we can't look at his humiliation of Hermione as any evidence of his motives, because it's not actually his move.