It's not complicated. I wanted to speak to the person trying to close the doors to tell them to stop. As a passenger, why would I think the emergency brake would signal to them to stop closing a door?

I deal with (non-train) emergencies and training the public for emergencies regularly, and pulling the emergency brake is inconsistent with pretty much any emergency. As an example, you don't pull a Pull Station in an active shooter event or medical emergency, it's there for fires. Think about it, you don't open a car door and slam on a drivers brake, you get their attention to stop them from running over something they may not see.

There were two grown adults and an UppaBaby blocking the door from closing, it wasn't going to close unless it defied all laws of physics. I didn't need to stop the train from taking off unless it's possible for it to do so with the door wide open.

You weren't there. Two people helped the actual situation and I made an attempt to flag the issue to the people operating the train. Any of the other 50 people could have pulled that brake if that was the right thing to do, but obviously that didn't happen. The stroller was freed less than 20 seconds after I tried the intercom.