Veterinarians have evening hours.
Your kitten won't be able to disturb the whole movie with its crying. Hell, you don't even have to take the kitten with you, and if you don't, you don't even have to worry about whether or not the sitter is available tonight. Your kitten won't grow out of those cute but expensive clothes within three months. Kittens look cute if they haven't had a bath in a month. You probably don't have to lie awake nights wondering how you're going to finance your kitten's college education.