Yeah but what if it goes lead flop / fish folds / reg raises? Then he could be doing that with hands that crush us and with draws. What do we do then?
edit: I'd think it's probably a fold as well because we have some edge on the draws but we are totally crushed by the rest of his range (sets, two pairs, straights, AQ).
re-edit: but yeah, what you said totally makes sense: betting gets value from the fish and forces the reg to play his hand face up.