Is it wrong to treat others the way we would want to be treated?

In general, the Golden Rule would change the entire world if we all lived by it. Obviously it doesn't mean that if you prefer strawberries but your friend is allergic to them that you don't give them to him/her! It goes to the heart of a matter instead and is generally governed by common courtesy.

Only if you look at it in a completely idiotic way.

It means with a basic respect and dignity -- NOT like a thing, not meanly or cruelly.

It doesn't mean treating someone the way one wants to be treated in all details (such as a person who loves to cook requiring their partner to always cook for them, when the partner hates to cook -- that's not what is meant by that "rule.")

It isn't selfish at all.

The Golden Rule basically just means to put ourselves in someone else's shoes, and make sure that we are treating them in a way that we would like to treated; i.e., with respect and courtesy.

Interesting point, some people have masochistic "rape victim fantasies" (What the f*ck)... but these people should not rape others out of common courtesy.

But, most of the time, this is a pretty good guideline for human altruism.

That depends. Let's say if you were a masochist for instance, and you got great joy in whipping yourself in order to become "closer to god" Your neighbor might not feel the same way......