Calling something a blind spot isn’t a disparaging reference to blindness. It’s referring to something about how sighted people’s vision works.
There are points in a sighted person’s field of vision where they’re not actually seeing things, but they think they are because their brain is filling in details. There are situations in which it is very important to be aware of this and intentionally look places where your brain is tricking you into thinking you’re already looking.
When sighted people learn to drive, they have to learn how to intentionally check blind spots in order avoid crashes. A sighted person’s brain will tell them that they’re already seeing things in those blind spots, and so they have to learn to intentionally look.
Calling something a blind spot metaphorically is a reference to this fact about how sighted people’s vision works. It means something like “you think you’re already seeing that, but you’re not. You need to learn how to look at it directly, or you’re going to hurt people.”