I agree it's not that simple, and you have a valid point. My position, based almost purely on speculation, is that you are looking a moving target because of the number of variables. I don't think it's a solvable problem to figure out where that point is. You would have to estimate it based on contexts and expected behavior. Expected aggregate behavior based on individuals' reaction to whatever the rates do.
However, by reducing the concept itself to a simple illustration, it still holds that a peak (or two or more) must exist. I don't know whether the (real) Laffer Curve is parabolic, a bell curve, or rectangular. It's only somewhat relavant to the point I'm trying to make. What the simple illustration does do is:
1. Show that revenues will not necessarily coincide or correlate with rates. Historically they have not at all times - especially during the four major rate cuts over the past century. (BTW I do not believe tax cuts for anyone are a panacea and I do believe that existing loopholes that allow GE and other hand-picked government favorites to pay no taxes should be eliminated, and yes I am obviously a staunch conservative - not a lock-step party hack).
2. Show that there exists at any given time a maximum revenue that can be obtained.
3. Infer that if spending stays above that maximum, then there is no solution to paying off the debt no matter what you do with tax rates.
Without solving that fundamental crisis, the system as we know it must crash. The longer we kick the can down the road on entitlements (including my SS, which I'm not counting on and coming up faster than I want it to), the harder the crash will be and the more dire things will be for my own children. The programs, as they exist now cannot possibly be sustained. Either we go back to square 1 by our choice, or we have that choice made for us by those who hold the notes on the debt.
Here's a question for people: do Bill Gates, Warren Buffet, George Bush, and Matt Damon deserve Social Security and Medicare? If so, why? If not, why not? (Note: assuming they reach the age, they are, of course, entitled to it).