The problem is that it's hard for most people to tell if someone's capable and belongs on the team in the first few months. Since ability and contribution are hard to measure, most human groups assess people based on shared suffering ("being a team player"). That creates a lot of the vacation-hostility that, after a while, people start internalizing. It's ridiculously stupid and utterly counterproductive. Total productivity is actually maximized (for most of the work we do) around 6 weeks off per year.