Some cats are more outgoing with inquisitive personalities, the need to meet every guest who comes by your house, and the insatiable desire for affection.
If your cat is one of those more outgoing types who doesn't scare easily, then it may be fine to dress them up in a Halloween costume, especially if they've been used to it since they were a little kitten.
But if you have a more sensitive and skittish cat, you may want to think twice. Some cats shy away from too much contact and can get overstimulated really easily. If your cat isn't the type to relish a lot of pets, and if they run and hide when the doorbell rings, you might not want to make them even more upset by dressing them up. Since it's Halloween, you'll likely get a lot of neighbors ringing the doorbell. So don't make an anxious cat even more upset by adding a costume to the mix.