Social conventions have their place. Jesus eats with the dismissible, those deemed unimportant. He would gladly eat with the successful, the powerful, too, but they don't want to rub shoulders with the dismissible. He eats as well with the irreligious. He would gladly eat with the religious too, but they can't stomach the thought that their reward is no greater than the reward of those who have made no religious effort at all.
Social conventions are a way of ordering society.
They have their place. Social convention and the Kingdom of God are simply not the same. Then it's quite plain that either we cling to the social conventions, assuming that the social order they point to is ultimate, or in the presence of Jesus Christ we look beyond social convention to embrace ardently the King who has embraced us already. Either we regard social convention as ultimate or we abandon ourselves to the rule of God exemplified in a welcome we are never going to find anywhere else. It is rather the case that all such distinctions and categories and evaluations and pigeonholes are left behind as we forget them in favour of a kingdom which transcends them.