The problem is "arms at your side" is subjective as well. How tightly do they have to be at your side? Do they have to be so tight that if we stuck a piece of charcoal in there a diamond would fall out? Or no daylight visible between the arm and the body? From what angle? And a referee is supposed to judge this in a fraction of a second? My argument here is reducto ad absurdium on purpose, to show that you can't remove subjectivity from handball calls. The only semi-appealing solution is to go back to what the rule originally stated (but apparently nobody cares about any more): the handball must be deliberate. I realize that doesn't remove the subjectivity, but much like the legal system, I would rather see a few guilty parties get away with it instead of seeing one innocent party (like Tony) get punished.
The Laws of the Game and instructions to referees are written in jargon and so some words and phrases have specialized definitions. Just like "gaining an advantage" in Law 11 has a narrowly defined definitionm "deliberate" and "intentional" do not mean the same thing. Beltran moved his arm to break his fall, not to protect his body from the ball. Instead of avoiding contact he moved his arm into the ball's path. His arm moved where he wanted it to go so the USSF definition of "deliberate" was met. I'm not saying that the call was right (as in just), but it does follow the instructions referees receive. The "bad calls" where the ref correctly follows the directions he is given but the call is obviously wrong (as in unjust) are among the ones that bother me the most. The fans, coaches, and players are outraged and they take it out of the referee, while the powers that give the guidelines face no consequences. Grrr.
When in the box, Tanaka actually clasps his hands behind his back. He might be the only MLS player I've seen who literally plays per the rule. If more did, there would be less confusion and more goals scored.