First, for every university-educated person we lose to the US we gain four from other countries. In fact, emigration to the US in the1990s is actually below historical averages. Taxes ranked 18th - just above free parking. With American companies paying up to twice as much to their high-tech employees it's a wonder we don't lose more. In fact, tax cuts actually contribute to the brain drain.
Tax cuts mean less revenue.
Most Canadians heading south of the border are medical professionals laid off due to funding cuts to medicare. Another argument the tax-cutters use is that if we cut taxes of wealthy people they will invest more and we will all gain as a result. This, too, is a false argument. When it comes to new, productive investment tax levels play a small role in companies' decision making. Most high-income earners will simply invest their tax cut windfall in the stock market which is scarcely different than casino gambling.