If you're out walking and you come upon a large dog lose that comes running up to you, of course you're apprehensive of this dog. You rightly so worry that it might try to harm you, you do try to be on your defensive. And the dog in turn, if it has a clue, does the same with you. And you don't dislike the dog for that. You don't hold it against the dog that it doesn't just assume the best of you.
If you go to pet it and stumble over your own feet and it mistakes your sudden movement for an attempt at aggression, the dog then thinks you're a bad person who will try to harm it.
If this happens, you don't hold it against the dog. Such is life.
Should it be so very different with people? It shouldn't. The world is full of hate and indifference. Of course we shouldn't be just assuming the best with people... Of course we shouldn't just expect others to assume the best of us...
Why would we do otherwise?
Assuming the best of others is the civilized thing to do. It's insulting to quickly suspect ugly things of people.
And if you're an idealist, then you just don't want to face the truth of this world. You want to believe that people are good and you want to deal with them as if they are.
And... you want the same in return. Which you're not going to get. And you're going to get insulted, etc that others aren't making such bizarre and idealistic assumptions about yourself; that instead people will quickly dismiss you as a bad person if you stumble over your shoe.
You will also be annoyed that you're expected to spend so much time doing the human equivalent of dog butt sniffing with people instead of getting beyond such barbarism and into actually interesting talk. But, you sure as hell better spend all your time on such crap as otherwise you're actions will be misinterpreted, you will be dismissed as a bad person.
Feh. Tired.