In many instances there are alternatives. Amsterdam to Berlin is served by good rail (except when DB are crappy) and flight options. NYC to DC or Boston. Maybe, someday, SF to LA, and others.

But even more people can

Just stop subsidizing flying, maybe even tax the fuel a fraction of the value it’s destroying and I bet most of flying will suddenly turn out to actually be completely avoidable.

We should be careful not to confound a call to reduce with a call to eliminate. I don't think most people want to completely abolish modern air travel.