I agree with all PPs that he is behaving very badlyand that you are absolutely right to stand up to him. If there are others in the group who are also fed up with them it may be worth enlistingtheir support. evwen 2-3 people all saying the 'No' to his mooching will help make it harder for this to be framed as you being the bad guy.
I would also suggest that for future events that you are hosting / organising - don't invite him. Even if you are only inviting members of the group, you don't have to invite *all* the members.
(and if asked why, you have a ready made answer "Well, Moocher is never able to contribute his sahre of the cost / food. I don't want to embarrass him by asking him for something he feels he can't afford, and of course, it would be grossly unfair to eveyone else to expect them to subsidise him, or to let him come without contributing the way eveyone else does")
Where practical, you can also get around this by sorting out money in advance - it's harder to mooch if you're being asked to pony up 3 days before the event, rather than at the ticket barrier .
It's harder with a party - you could try giving very specific assignments (e.g Moocher's invitation says clearly he is responsible for bringing 3 large pizzas, or a 12-pack of beer, rather than eveyone being asked to bring something. And if he shows up without , tell him that he needs to sort it out. and don't let him in if he does not.
If challenged by other members of the group, be firm. Tell them that they are free to support Moocher if they wish, but that you are done supporting him, as it is never reciprocal. He does not pay back people who cover him. Say explicitily that it is unfair for him to be taking from eveyone and never payi ng back, either in cash or kind. And if you are critisied, keep repeating that. "Why are you blaming me? Please explain why you feel I should be paying for Moocher's fun? Why are you not having this conversation with Moocher about his lack of contribution? It feels very unfair that I am being bullied for standing up to someone who is, in effect, stealing from us, individually and as a group , by never paying his way."
Don't be embarrassed about calling him out. He is the one who should be embarrassed, not you. The same goes for univited people showing up. HE is the one who has been rude, to you as host, and to the uninvited guest. I think in those circumstances you can say to the univited "guest" "I'm so sorry I can't invite you in. as moocher knows[/i], this event is strictly invitation only and it was made clear to all invitees that no extra could be accommodated. I can't make any exceptions as it wouldn't be fair to other guests, who would have liked to bring extra people, to let you in." It's Moocher's problem, let him deal with it.