[JohnG]

It's an auto call, normally. For these ratios, on this flop, a typical player can just be going with his hand because he can't just call. He can have plenty of hands you bury, hoping you have AK and missed. And even more so if he thinks you can fold KK. It would be correct to raise you with any hand in that case. Of course, against players that just call with pairs on this ratio, you can fold.

An opponent has to get very lucky to flop a set on you when it's headsup seeing flop. Odds are he has a hand you bury like a lower pair or a bluff.