It’s fun in the same way losing a game is fun. Its fine in moderation, horrible in excess or when one sided. It’s still sonething you want to avoid, but not so unpleasant that I woukd want the game made of it to stop.
People who don’t respect a hard no are not cool. But I also feel as though I am missing out when I’m with someone who I am close enough to tickle, but they won’t tolerate any tickling.