I think the part I object to most is the idea that if someone states that they might not want or be able to participate in 100% of the planned activities, then they are not permitted to attend.

That's particularly true given that this trip coordinator was not able to give me a clear itinerary for the trip at the time she expected me to provide a deposit.

How can I commit to attend every activity, when they can't provide me with a list of what every activity is going to be?

How can I, as an adult, commit to a trip where I don't have veto power over specific activities if I have a migraine, or if I simply need a break?

This kind of attitude robs a person of their full humanity. It insists that participation requires giving up control over ourselves to the trip leaders. It's a situation rife for abuse.

In real life, people need things to get along!

People need antidepressants. People need breaks. People need veto power.

That doesn't make us bad people. It makes us human. It makes us better adults.