Bad example in the OP. Beltran was going on first movement -- he didn't take a big secondary & get "deceived".

So, assuming that MLB wants to make this old standby move illegal, how would they change the rule.

I assume they would make it illegal to feint to any base, not just first, so the pitcher would have to throw on any move to a base. Seems like this would cause much more problems, not asllowing a fent to second to drive back a runner without F4/F6 being at the base to receive the throw. Seems to me the medicine will be worse than the illness...

No, feints to 2B and 3B will still be legal. See 8.05c COMMENT: where it says "This is legal," insert "not." Problem solved.

Not what I read... where I first saw this stated that they would make feints to any base illegal.

Then again ... why are feints to 2nd and 3rd ok, but not to first. Other than tradition, it seems an odd exception.

Because there would be runners diving back to first 5 times in each at bat on fakes to first. I'm thinking that it would drastically reduce the number of stolen bases.

A lead off first is vital and the pitcher has huge incentive to keep the runner close. Off second and third? Not so much.

Well, you answered the opposite of my question.

Why is it OK to feint to 3rd? Or 2nd? It might be less critical to hold a runner there, but if a pitcher is going to take the time to decide not to pitch and instead stride toward a base, obviously holding the runner was important enough. So why allow them to feint?

A baseball move is allowed until it's not.

The reason to prohibit feinting to 1B is that it's easier and more important to steal 2B than 3B or home, and harder to throw a runner out at 2B than 3B or home. Since these reasons apply only to 1B, it makes sense to limit the prohibition.

Prohibiting feinting to 1B gives a better balance of offense and defense.

In other news, it seems the minor league record for stolen bases is likely to be broken this year (145 — maybe they need to prohibit feinting in MiLB).