It's hardly a double standard. Fringe members of your own side cannot represent your entire group, because you are part of the group therefore you have 1st hand

It's hardly a double standard. Fringe members of your own side cannot represent your entire group, because you are part of the group therefore you have 1st hand evidence that some members (i.e. you) are utterly rationale, reasonable, realistic human beings. Considering your political opponents is difficult. You may not even know too many of them in real life, and even when you do---political discussion is frowned upon so at best you get a niggling thought of "Bob is a great dev, I don't understand how he could be so crazy to vote for X".