I am glad that you are asking the question. And maybe others, who also wonder, will have the truth about getting a bunny fixed or not. This goes for females bunnies....yes they SHOULD be spayed. Why? (1) to settle down the hormones, (2) for health issues. Female rabbits seem to have a high risk of developing uterine cancer (about 85%) (3) to not reproduce (4) for being clean. For males it's a bit different. They also need to be neutered for same reasons as (1), (3) and (4). However, a small % of male ARE clean (meaning they dont spray, they use the litter box and they are affectionnate). So if a un-fixed male is clean, it's YOUR choice to get him fix or not. My actual bunny, is 6 months old and he is clean. So I wont get him fix.
For your other concern. Fixing your bunny is NOT cruel. In fact, it will help them a lot. Most people here have they bunnies fixed. I think that having our bunnies fixed hurts more us then the bunny!
Anyways, I hope all that helps.