People can anticipate that their state is opening up and decide "it must be OK to be outside more, not wear a mask, etc."

They start exposing themselves to the virus weeks in advance and transmitting it to others

By the time of a formal opening announcement, we find the infection rate has already increased.

Covid19. If 60% of people never countered the disease, state and national politicians saying that the cure of a lockdown is worse than the disease carries a lot of weight with those people. Throw in seemingly healthy pinheads out protesting with guns and confederate flags, then it becomes harder for even responsible governors to keep their state locked down. So the infection rate increases due to behavior, like you implied.

What it will take is close to 100% of people knowing someone close to them that have died of covid19 or were seriously ill from it, unfortunately, by then the death toll is going to be massive.