Normally I'd Call But I Call Down Too Much

[moot]

It's not so much a bad fold, as it is a bad river bet to begin with.

For instance, after you were raised on the end, if someone brought me in and gave me the choice between calling the raise or folding, I would be likely to choose folding as the +EV play.

BUT, if someone brought me in on the river, before any of the action, I would have choosen check-calling as the best play.

First of all there's the psychological factor. It's just not mentally fun or healthy for me to have to lay down trips with a decent kicker for one bet on the end (after I'm raised).

Addtionally... by checking he might value bet a lower pocket pair, seeing the two aces and figuring you're less likely to have one.

But when you bet he's very unlikely to raise with anything that you beat. Plus he might be able to get away from a hand he otherwise might have value bet on the end.