This pot is 14BB when it makes it to Hero.

Hero only needs to increase his equity by less than 7% to make this raise correct.

If you assume that MP3 is WAY more likely to have 2 pair or even just a flush or straight draw, than he is to have flopped a straight -

Lone K.
AK.
Bottom pair.
Next to bottom pair
Second pair.
Weak top pair.

If Hero folds ANY ONE of these hands, the raise was worth it.

Even if one person does have an 8.

For every hand that folds, Hero increases his equity by 1.5% for when one of the 3 remaining 8's falls on the river. He also gains ~5% equity by folding a lone K.

Just because we now know what people held, doesn't make the raise incorrect at the time.