Even Slate, which is hardly a right-wing bastion, concedes that there is an effect (http://www.slate.com/articles/news_and_politics/explainer/20...)
If we subjected you to a 99% tax rate tomorrow, would you work less than before? A yes answer is all that is needed to concede the point theoretically. Then, we're just arguing about magnitude. And I just don't believe you if you answer no: Who is going to work a full-time $50,000 a year job when they're only taking home $500/year?
For further reading, Paul Graham has argued that redistribution through higher tax rates leas to less entrepreneurship (http://www.paulgraham.com/inequality.html)