The idea that people wouldn't think discrimination is evil without government intervention is frankly insulting to my intelligence.
Well, that's lucky, isn't it.
The issue isn't what people think. The issue is enforcement. Only the state (in one form or other) has the power to enforce public disgust against certain practices in a way that doesn't cause serious damage to social order.
That sounds nice and all, but is utterly meaningless.
I think you'll find that when discrimination against the disabled (and countless other minorities) was legal, incidents of such boycotts and pickets were somewhat on the rare side.