Health insurance. UnitedHealth has a blatant vertical monopoly that needs to be dealt with.

To add info, Optum is owned by United. So, you could see your provider at an Optum Clinic, get a prescription from OptumRx, pay your co-pays with your OptumBank HSA, and, of course, your insurance is from United Health. So, literally no part of that interaction left the UnitedHealth ecosystem. And they claimed a profit from every single one of those interactions.