I think the issue is kinda obvious.
-Valve is an American company
-Americans are known for having an abject dislike of porn in plain sight
-The game developer of "Seduce Me", by their own admission, didn't bother to actually check with Valve to see if it would be alright to put their game up, and instead just assumed
"I think we'd managed to convince ourselves that there was a reasonable chance that they'd take it, and the game was close enough to being finished when Greenlight came around, so we thought we'd get in at the start and see what the community said."
-The people on Steam got pissed, as any sane person would know they would.
-Valve pulled the game because of user backlash to it.
The removal of the game sits SOLELY on the lap of the developers of "Seduce Me" who made an asinine assumption without actually bothering to check before hand if their assumption was right, and then had to face the consequences of their wrong assumption.
As they say "assuming only makes an ass out of you and me", Valve only looks like dicks because of "Seduce me" Developer's assumption, and I don't believe Valve has to explain themselves in a situation that was caused by SOMEONE ELSE's stupidity.
If anything, the people who made "Seduce Me" should have to explain why on earth they thought, when all other past evidence of American companies actions and culture shows otherwise, that Steam would accept their game.