You're consenting to have your mind attacked with all the mental weapons at someone's disposal. This is a lot scarier because you're willingly giving up some measure of control over your state to the other person, however difficult it may be for them. You're also being attacked as yourself. The AI player is playing a role, and attacking within that role. Their own mental wellbeing is a lot less at risk, unless they think they've got horrible depths they never want to sink to.
to make a shitty analogy: It's like being at the top of a tower while someone tries to knock it down with their bare hands. Even if they have very little chance and have to expend a lot more effort than you, you're the one who's risking the greatest pain
Their own mental wellbeing is a lot less at risk, unless they think they've got horrible depths they never want to sink to.
If I remember right, that was at least part of why Eliezer stopped playing in the first place. Manifesting as a sociopath is non-trivial and invites some fairly heavy cognitive dissonance.
Update 2013-09-05.
I have since played two more AI box experiments after this one, winning both.
Update 2013-12-30:
I have lost two more AI box experiments, and won two more. Current Record is 3 Wins, 3 Losses.