Technically, isn't what Clarence did legal because the ethics rules weren't in place at the time?

Frankly, only fools believe in ethics anymore. There is only a personal cost to having them that causes you to lose time after time in life.

Having ethical standards is basically chopping off your arm at this point.

Clarence Thomas is a good legal thinker and is worth having on the court. He has a very specific world view that I don't think he would be likely to defect against. The only real argument that might work is deterrence, but that's probably not worth it.