how many more passengers would they carry, how much larger would the profits be, if the company acted in a reasonable, friendly and ethical manner toward its staff and customers?
They wouldn't, because that's not their business model. They offer what appears to be a lower fare than their rivals and then use their devious tactics to squeeze the last drop of revenue from ancillary services. It's all stated in their Ts &Cs, which many people fail to read, and they comply with regulatory standards, but only just.
If they operated differently, their fares would go up and they would lose market share. Also worth pointing out that on many routes they have no competition, another smart move.
Whatever one might think of O'Leary, he is no fool!