Is it? Why is it so hard to imagine that higher taxes on risky ventures might cause somebody to go "Eh, not worth it, I can make better use of my time - like spending it with friends and family"?
Most businesses fail anyway and knowing that even if you beat the odds and succeed, the reward might not be worth it because the government takes an ever large cut should give every reasonable person pause to reevaluate their life priorities.
As cliche as it sounds, money isn't everything.
I can't wait to read about all the entrepreneurs who come out and tell their story about how the tax rate at the highest level impacted their decision to create a startup. I'll be waiting forever.