As played, I'm ok with hero's smooth call on the turn. He's wa/wb, and theres almost no river card that can come that changes his holding. If he's behind, he's behind and he's getting stacked and there is nothing he can do about that. But if he's ahead, villain is betting very hard with probably two outs at best, and possibly bluffing. No reason to discourage villain from doing so.

But I still raise the flop.