Is driving with 2 front wheels not equally weared out bad for the car?

It could give a loss of directional control, mostly during braking. If you've got any kind of computer aided braking, you could seriously confuse the system. I don't see a looming disaster, but I would bite the bullet and replace both, if that's the thrust of the question.

I would want to know why the wear is uneven. Perhaps the steering needs lining up, or something is broken in the suspension. Could be dangerous or illegal to drive like that.

I have a Corolla 1990, very old car. When I bought the car, the front tires are already uneven, and I had it for 3 years. Should I buy different used tires which are the same wear out?