A lot of arguments see to be that it tastes better. I don’t want to argue subjective tastes. However, in terms of economics, the better taste would mean that there is no need to subsidize it. The market would bear the additional cost if the taste and utility of milk is there. The question posed is still relevant: why do we subsidize it? Everyone arguing how much better it is than the alternatives are just proving the point that we shouldn’t be subsidizing it.
I don’t think there is a proper way to ask. Leave people that are eating alone so they can enjoy their meal. Even if you ask nicely, you are still putting pressure on the person eating. If you need to be seated a specific time go to a restaurant with reservations.