First of all, the odds on a player having the exact amount necessary for a straddle are remote. I disagree with both of you because you are restricting the same action from any player that might have slightly more than the straddle, but not enough to complete a full raise. Example: What if the UTG player had 25 instead of 20...would you allow a straddle? If so, why? What's the difference?
A straddle is nothing more than a "blind raise" before cards are dealt. I've never seen anything in writing that insists that a straddle can only be executed if that player can reopen raising when the bet returns to him. You can't look at your cards and then straddle...so I see no reason for preventing others from raising, if they desire.
Nick -
I agree with your point that the chance of someone having exactly 2 big blinds under the gun are remote, and even more remote that he'd chose to say "Straddle" rather than "Raise".
Yes, a straddle is nothing more than a blind raise,
with the opportunity to re-raise.
My point is, if he does not have additional chips to exercise that opportunity to re-raise, then his blind raise is just that - a raise, not a straddle.
Some of your other points are just completely wrong.
How does our decision restrict others who may have slightly more than 2 big blinds?
If he has 25 instead of 20? Yep, allow a straddle. Sure, it defies good strategy, but certainly valid. The fact that such a partial re-raise would not re-open the raise opportunity to those that called is irrelevant.
Prevent others from raising? How does the straddle prevent others from raising?
You've never seen anything that insists that a straddle can only be executed if that player can re-open raising when the bet returns to him? Me neither. That's not what I'm saying.
I'm saying that to straddle, the player must have at least one chip behind, so he has an option to raise, even if that raise is too small to re-open betting to players that merely called the straddle.