Coursework in legal matters is part of educational leadership/administration programs and is a focus of professional development, in part because districts are incentivized to reduce litigation costs.

I share your apparent concern that districts, etc, screw up discipline often and unjust outcomes occur. However, doing nothing isn't an option, and I don't think punting more of school discipline to the police is likely to improve outcomes.

You'll find both administrators and SRO's abusing their powers, but I think the SRO potential for abuses are larger.