Originally Posted by
jsloan
UA should block off seats at the back of the airplane for assignment at the gate, which would limit this sort of problem.
They do. A number of seats are held for assignment at the airport to accomodate families, disabled passengers, and other issues. On most flights, that is enough to resolve such seating issues as was the case on the OP's second leg.
For whatever reason, it isn't always enough. There will always be situations where all of these passenger needs can't be addressed with the remaining open and blocked seats and it isn't only because of BE fares. Airplane swaps, misconnects, flight cancellations, and other unrelated (to BE) issues can result in these seating issues where the agent is left with no options short of moving other passengers who already have their assigned seats.
There are steps that a passenger can take at booking to minimize the chances of being caught in this situation but, even that, isn't guaranteed as cancellations, misconnects, etc., can disrupt the plan.
The airline could block even more seats from assignment, and maybe they should. That would reduce the frequency of such problems but they'll still occur. I have no idea what the proper amount of block seats would be and what the impact of the reduction is seats available for pre-selection would be on other passengers. You wouldn't want to overdo it and end up with a lot of passenger who needlessly have to wait to have their seats assigned at the gate.
The only way to guarantee that these situations will not go unresolved is to allow the gate agents to unseat other passengers in order to keep families together. Is that what we want? How would it be limited and controlled? What would be owed to the displaced passengers?