Cmoonbeam, I'm sorry that you're dad's giving you hell about this. Also, sorry that this emotional bomb just fell on your lap.
There are some people in the world that are CONSTANTLY ignorant. and they're ignorant about everything and everyone.
However,
With you dad, I don't feel that's the case.
If a parent has a child who got diagnosed with a serious disease, that parent goes a little nuts. There's no way around it. Your father is not trying to convince YOU that aspergers doesn't exist, he's trying to convince HIMSELF. If the parent can fight the notion that aspergers exists then->there kid isn't sick. It's a break in logic and parents go a little nuts.
Here's another example and it's the same thing:
A father runs into an emergency room after being called and told his son was in a serious car wreck. The son is missing limbs, he has serious brain damage that is unreverseable, his organs are failing left and right and ANYONE could plainly see the son has only a few hours to live. The father asks, "so what are you going to do doctor? FIX MY SON! SAVE HIM!" This is a true story, my brother and father are doctors. The father can't accept that his son is sick and dying.
In both cases yours and the car accident, the father loves the son soo much that the very thought of his son being hurt is... well the father loses it and goes nuts, can't handle it.
I hope this gives you understanding to forgive your father a bit. He's acting like a fool no doubt but it comes from love. Your father is a human being with faults but he loves you.
Perhaps level with him, 'dad I'm just as scared as you are.' That might bring him back to reality or sanity.