I agree, as long as we're talking lower base rates.  I think taxing cap gains at 35% or 39% would be excessive (and really hurt investment), but if we're eliminating deductions/breaks/credits and lowering the top rate to something like 20% or 25% max, then I'd say tax all types of income the same as you say.

Of course, I'd go even further than that if it were up to me... do all that AND lower income tax rates even further, and then add a modest national sales tax.  Those are much harder for people to manipulate their way out of and around since it's across so many small transactions throughout the year.