It may be true that many or most people who stand for the chorus do not think of the act that way. But that does not mean that the act does not have that significance: it means only that those people act thoughtlessly, out of social conformity, and fail to think of the meaning of their actions.
I respect your opinion, but I don't understand why you bring such a high degree of passion to this matter. After all, there are many customs that most people just do without questioning its origin.
For instance, shaking hands started as a gesture to prove that men did not have a concealed weapon in their coat sleeve. A post-sneeze "God bless you" was said b/c it was believed that the person was purging demons from the body. Although people do not cater to those theories today, most still willinglly shake hands and say "God bless you" as commonplace gestures. And I guess that I'd approach the "Hallelujah stance" in the same way.
I consider myself a well-informed person that doesn't do things blindly, and at the same time I bring neither prejudice nor passion to these harmless customs; to do so would seem like "a rebel without a cause".
It was a "WTF?" moment for me when the audience rose to its feet at the "Hallelujah" chorus. When I learned that this was the custom, I resolved never to attend another performance again (or to leave before the performance got to that point). I felt utterly betrayed...
Again, I respect your right to follow your conscience. However, why deprive yourself of a wonderful musical experience?-- and for what result? Couldn't
your reason for standing be to just see the performers? Or, couldn't you, the "conscience objector", just remain seated with your eyes closed. Either way, you get to enjoy the purest form of "The kingdom of this world...", which is expressly what Handel intended for you and for all of us. I don't know if Handel would care if audiences sat or stood, but I'm sure he would not want anyone to boycott the Messiah or retreat to the lobby in the middle of a performance...
and for what??!!
So, given the fact that this particular custom is so inocuous, I think that you should always treat yourself to a live performance. (Damn me and all the other king's risers!)
I confess that I'm the sap who gets a charge from the trumpet solo and second strain of "King of kings, and Lord of Lords..." And there is no one-- no way, no where--that would rob me of that moment!