Theon has far more of a character defense than Jaime anyway despite the kids murder. Imprisoned his entire life, given up by his father only to be denied his family name upon return by that same father. Tried to redeem his name by sacking Winterfell, would have failed had they known Bran and Rickon escaped. Killed 2 peasants to cover his tracks. Despicable, yes, but what are Jaimes reasons? Oh yeah...."im a prick"
And I know show and book are separate yadda yadda yadda, but in the book Theon was convinced to murder the kids by a raging psychopath who took advantage of the difficult situation and manipulated him. That character was cut from the show though.
Granted, in the books Jaime never killed his cousin to escape, so I hesitate to hold that one against him. The characters in both formats would have to be examined differently.
But still.....fukk Jaime