When I host an event or have guests over to my home, how can I insist that they do not bring animal products to consume at the event? In particular, I am interested in how to handle ethical opposition to such products without appearing ungrateful for what they might bring, or forcing my views on them.
The host generally makes the rules for an event, so a condition like that is entirely appropriate. If they have dietary/medical needs that they feel cannot be met by vegan means, you might want to ask them to check with you
The way you explain the expectation is going to be entirely culture-dependent. One possibility is including verbiage along the lines of "Guests are encouraged to bring a dish to pass, but please limit yourself to vegan options."
Be warned, though, that with a restriction like this, some people may be turned off, or just decide it's less trouble to skip bringing a contribution. It might be less polarizing to allow non-vegan dishes, but encourage guests to label their dishes if they contain non-vegan or potential allergens "due to dietary restrictions on the part of the host and/or other guests".
I believe it is. You are the host and you are offering them a place at your table. Unless there is a medical issue preventing someone to eat what you plan to cook (allergies, perhaps?) it would actually be inappropriate for them to bring their own food. I would say your best shot is to notify them about your intentions beforehand and see what they have to say about it. That way they can tell you their objections and you can judge whether they are serious enough for you to consider.
If someone asks you to explain your expectations, simply ask them whether they would require the host at an omnivore event to tailor their menu according to them, even against his beliefs (eg. demanding from muslim host to serve pork).
An example I usually call for when faced with this situation is responding "If you would invite people from a place where they eat dog and cat as much as they eat pork, would you serve dog and cat, or would you restrict your food options to those that you find appropriate yourself?". That usually does the trick. People who eat meat, invariably also eat non-meat foods. If nothing else, they will eat fries. But as others suggested, let your guests know before hand so they can grab a bite on the way to your place (as we all have done so often!).
As with the other comments and answers, it is your house, your party, basically your rules! However that comes across as a bit harsh when put like that. Most reasonable people will not have a problem with your requirements - in fact it is a perfect opportunity to educate them. Meat eaters often scoff at vegetarians, and vegans - mainly through ignorance of the 'product' itself. If you serve a great tasting, interesting and nutritious meal then, maybe, just maybe you have converted someone. If nothing else you may have broadened their horizons. Perhaps say something like 'Hey guys, I know you are not vegetarian, but please allow me to surpise you - tonight is a meat free zone!' If someone is not willing to stick by your rules, then do you really want them at your party?
I don't think you should force your guests to conform to your world view.
Every person is different and by insisting that they all be like you in your presence is intolerant and preachy. And the very thing you are seeking is for people to be tolerant of you and your personal choices.
Ideally your personal choices would make you stand out as different and people would ask you about it because they are curious why. Those are the best times to talk on an open and even field.
I didn't become a vegetarian because someone told me about an ethical issue I was in violation of, instead I quit associating with "those" people.
This is an ethical issue, and if you were to reverse the role and be honest you would see how rediculous it would be for you to be asked to eat meat at someone's wing night.
I have a beef farmer father in law and my mother and brothers think that it's impossible to have a meal without a quarter plate of meat.