[...] Not saying you can't hate her or that you don't have good reason for it. [He knows enough of what she does in the future to know that much]
[But it just doesn't sit right with him - to judge someone before they even did anything wrong, just because they could or might. This is an entirely unique situation, of course, with the time aspect -- and logically he gets Merlin's anger and discomfort with it. But it hits too close to home on the whole judging thing.]