You stand to win $0.42 at the expense $0.30 when you raise. It's as simple as that. You never (or rarely) make more than that.

Let's say you're ahead half the time. That means you make $0.06 every time you make this play [(1/2)*($0.42) + (1/2)*(-$0.30)].

Now say when you call he bets all his range on the turn for $0.18. Now you make $0.60 for your $0.30 (by calling the flop and turn) which is $0.15 every time you make this play [(1/2)*($0.60) + (1/2)*(-$0.30)]. It's not likely he can fire the river unless he's really strong, and if he does, you give up. But by just calling you let him bet with the half of his range that you beat on the turn.

Over-simplified, yes. But by doing what you're doing you're not really playing post-flop poker imo.

In response to one of the things you said, about not really thinking you're ahead: if he only ever leads top pair on the flop, you fold. If he never double-barrels, you know you're beat on the turn and give up there.

Likely scenario:

Flop:
MP1 bets $0.12, Hero calls $0.12
Turn:
MP1 bets $0.18, Hero calls $0.18
River:
MP1 checks, Hero checks.

> When this happens, you always make more than if you raise the flop.