Jon doesn't know how corruption works, but he assumes it's like what Hell can do to people. Even when it doesn't completely take their choices away, it makes them do or say things they wouldn't ordinarily. Corruption must be a more extreme version, but he knows it doesn't make it any easier to stomach her actions even the ones done while corrupted.

"Might not be something you can wrap your head around without living it."

And while he hopes she never has to live it, he also doesn't want her stuck in Hell forever.

"It seems like your friends don't hold what you did against you even if it might be harder for you."

To not hold it against herself. He understands that too.