First, so sorry that happened to you. That's just horrible.
I agree that bathrooms should be used as bathrooms, not for other stuff, but I don't think it's wrong to use the handicap stall.
I think first come first serve is fair. If all the stalls are full, I'm using the handicap stall. If I get cornered, I'll just call security. Whose to say I don't have to go as bad as the person sitting in the wheelchair or
scooter behind me in line? I don't understand where this idea comes from that just because you need the handicap stall, you shouldn't have to wait for it.
On the other hand, if anyone in line had an issue where they couldn't hold it, I'd let them go in front of me in line, weather that was for the handicap or a regular stall. I know little kids can have issues with that as well as people with hidden disabilities or ones who have been waiting a long time already because of someone misusing the handicap stall to change in.
We have Crohn's in our family, so bathrooms are a big deal to us, and I promise you that you'd rather wait for us to use the handicap stall, then have us go in the middle of waiting in line. Also, I know a lot of people with Crohn's will play on their phones while in the bathroom because you can get stuck in the stall for such a long time, so just because someone has their phone out doesn't mean they are just wasting time. We don't talk on them except to reply yes still in here when someone gets worried we are lost, and we wash them after, along with our hands.
Personally, I think people needing the handicap stall just need to remember that there are other people who may need to use it for differing reasons that may not be obvious, so please don't freak out on them when they do. I also think Disney needs to build more handicap stalls.