You can think of it in terms of how many streets of value your hand is worth. From the turn forward, your hand is probably worth something around 1 bet on average. So you could call one street, but not two. If you're in position and it's checked to you on both turn and river, you could possibly consider a value bet. But if anything more than one bet goes in, then you're probably putting money in bad.

Of course, this can easily change depending on player tendencies. Against some players, your hand may be worth zero bets on average. And as you noticed, players can very easily have a flush there more than half the time, and you don't have a particularly effective bluff catcher. A lot of the time you can probably x/f your straight without it being a significant problem.