I understand that it might be a great service from UA to offer gate-check to passengers and that UA may have all the good intention to encourage or promote the free gate-check service. Sometimes the agent will stand by the entrance and request passengers to gate-check their carry-ons or bags so that the gate can be closed for on-time departure. As usual I always travelled light with a laptop backpack and a small carry-on bag (< 1.5 ft in length). Yesterday I was sitting 5C in the first-class cabin (B757-200/24 FC seats), but unfortunately I was the last person boarding on this short flight.

An agent by the door: ‘all overhead bins are full and closed. You must gate-check your carry-ons to get on the flight.’
5C: ‘I have my computer and small bag. I can put under the seat’
Agent: ‘No, you can’t. Do not argue with me’.
5C: ‘but they will fit under the seat. My backpack has a computer. My small bag has crystal glasses. You really want me to check my bags?’
Agent: ‘No gate-check. No flight. You are holding the flight.’

At the end, the agent took away my small bag, but the other agent let me carry my laptop backpack. When I arrived at my destination and got my bag from the baggage claim, I immediately opened the bag, two small crystal glasses were broken in pieces.

Am I justified to be upset?