This is completely valid, but if you go hunting for an IP block that has never been used for spam at this point you're going to be looking for a long time. It should not be the #1 consideration when choosing a hosting provider just because someone abused their IP block in the past (possibly before they even owned it). In any case, trying to run mail off a VPS would be stupid and that's not what I'm saying. I'm saying we don't all need to capitulate to paying Amazon or Google to forward our outbound mail, and it would be better if we did not, even considering the struggles attached to bucking the trend.