Well, thing about Sandman is he's a character of convenience. He doesn't commit crime because of some psychotic compulsion, and he wasn't a hero because of some higher moral calling.
He played the role that was most convenient for him at the time. To tell the truth though, I really don't understand his return to villainy. It just doesn't jibe with the character's development. He had gained trust, and a lucrative career as one of Silver Sable's mercenaries.
Why turn his back on that for a life of petty crime once more? One story idea I have kicking around my head is one in which Silver Sable contacts Sandman once more for a contract job. I haven't gotten much concrete details beyond that, but one concept I wanted to explore was that Sandman actually was there when Scarlet Witch was going nuts and Disassembling the Avengers. He wasn't in the thick of things, but rather watching from the sidelines, conflicted about what to do. And the only one who noticed this was Sable.
Over the course of this job, he would come to realize that he had it good with Sable, that it was both a convenient job and a good way for him to make some kind of a positive impact on the world, even if it's just bringing down criminal scumbags for money.