Wether or not a Convention for this or that is 'necessary' is just an odd question. It's not like we can only have a limited number of conventions a year, thus we must only choose conventions that are, well, conventional.
Having a fun and open event where LGBT topics in gaming can be discussed, or an event where gay (and straight couples!) can hold hands while they peruse the artist alley without fear of being pointed out is a good enough reason to hold these kinds of events. Even if it wasn't, People who want to go to them will still go to them, regardless of what others people think and therefore should do. You don't make decisions for anyone, only yourself.
Having a fun and open event where LGBT topics in gaming can be discussed, or an event where gay (and straight couples!) can hold hands while they peruse the artist alley without fear of being pointed out is a good enough reason to hold these kinds of events. Even if it wasn't, People who want to go to them will still go to them, regardless of what others people think and therefore should do. You don't make decisions for anyone, only yourself.