I suppose some would argue that love is what makes tolerance possible. But with love comes expectations, which, when violated turns it into hatred. (Hatred is just disappointed love. You can't hate someone you don't love; the actual opposite of love is indifference).

I think tolerance comes from accepting that there is strength and interest in diversity, that tribalism is a primitive dead-end, and that community transcends difference. And then it's just a lifetime of working against the tribal, me vs them mentality that natural selection has bestowed us with. That's a tall, but doable, order.