was it popular opinion that black people were being discriminated against?

It was not opinion, it was fact. And still is. I lived in Texas for 7 years, I can give you plenty of examples if you like. As it becomes less socially acceptable, racists have also become more insidious.

in order for a gay person to be discriminated against on the level you were illustrating

The point of the analogy is that economic violence is possible.

Having established it as possible, it doesn't require an extreme instance, like all bakers refusing service, or a physical wall around your property.

For example, suppose there are 10 bakers in my city, competing to my benefit per our Lassiez Faire economic system. One baker refuses me service based on my class (black, gay). Now there are 9 bakers competing for my money. Not only is competition reduced, harming me economically, but I have less selection. I really liked a cake that bigotted baker won't sell me.

Now, that's far less harmful than all 10 bakers, or a wall around my house. But I have still been economically harmed, to some small degree. By refusing to provide me service based on my class, the baker has committed economic violence against me.

Ergo, I believe the law should recognize economic violence, and make significant acts of it illegal. Yes, you could come up with ridiculous examples. The baker has harmed me economically by refusing to make a cake with dicks on it for my flamboyantly gay wedding. I'm not arguing for extreme laws against any conceivable harm to the slightest degree. But I do believe the law of a Free government should recognize the concept. And that's exactly what anti-discrimination laws do.