I know you are dead set on this point but your example is different than enforcing mask wearing and social distancing
If a guest is sitting down to ride an attraction a) they have been in line for an xx amount of time b) want to ride this ride. IF they decide they don't want to use the safety belt/lapbar/restraint the entire ride has to stop. Socially this person will feel the pressure to buckle up or leave. This scenario has happened but is very, very rare
Obvious pregnant person goes to ride an attraction that is clearly marked as not suitable for women who are pregnant, CM cannot ask this person not to ride, they (CM) are told that the warning sign is there and it's at the risk of the pregnant lady. She's not endangering anyone else but herself.
The mask/social distancing will be see as scenario 2, endangering yourself more than endangering others, unfortunately. IF Disney decides to impose the rule it'll be up to Disney security and OC Sheriff to have the final word.
Unfortunately is the way it is and CM already know that if masks are going to be mandatory they have to buckle up for the complaints and the fights, they go into work every day thinking, who is going to yell at me today? it's sad, but that is the mentality of the front of the line CM because people have become extremely entitled