Personally, I am okay with someone leaving a line to run to the bathroom. If the line is really long, it can be difficult... sometimes as we get older it is not that simple to just hold it. If you come up on a long line, it is probably a good idea to use the restroom before you get in the line but, what if like someone said in this thread you start a line that is suppose to be an hour, and it turns into 3? In the Florida heat, trying to stay hydrated, I would think a 3 hour wait with no bathroom break would be difficult for a good many people.
My thought is that if someone leaves the line to use the bathroom.. fine, totally understandable.. now if they are leaving the line to go to the gift shop, or kill time so they don't have to stand there, that is not okay with me. I am also not okay with family members holding places in line for any length of time. Leaving a line to use a bathroom is fine, never standing in the line to begin with and then coming up to meet family, is not okay. My attitude is the person should be standing in the line the vast majority of the time, just like everyone else but, a bathroom break is something that should be excused.