Well, sure, repeating the multiplication table or the digits of Pi every day can be quite useful. It helps you memorize products of single-digit numbers and also Pi.

But repeating a pledge to obey an institution is, IMO, irrational at best. Imagine that the United States did something insane (well, more insane than all the things it's doing right now), like starting World War III with no provocation whatsoever. Would it still be deserving of your allegiance ? That is to say, would you still do your best to uphold its principles and further its goals, which now include "kill everyone on Earth with nukes" ?

Now, if the Pledge said something like, "I pledge to support those institutions who have a reasonably good chance of improving the lives of all humans, and to reform or abolish those institutions that hinder progress toward this goal", then I could probably get behind it.

Similarly, I wouldn't pledge to drive my current car to work every day, be it rain, hail, or shine -- but I could reasonably promise to stick with my car while it functions, fix it when it breaks down if fixing it is financially feasible, or get a new car if I can afford it. Such an oath may not sound as solemn, but at least it's practical.