I'm mad at my friend for driving recklessly on a snowy road.
How were they driving recklessly?
They were driving as if the road was clear and dry.
Yes, you shouldn't drive recklessly in bad weather. That's one way to get into an accident and hurt yourself or others.
I agree, they shouldn't have driven.
I am glad that you care about your friends enough to tell them to be careful on the road. Not only could something happen to you but so could happen to somebody else on the road.