At recent performances of Messiah, the audiences readily stood during the Hallelujah chorus. During my pre-concert talk, I suggested that the tradition may have started when King George II stood thinking that he was hearing his country's national anthem (Rule Brittania). They do start similarly, in identical rhythm. (Maestro Rick Coffey respectfully disagrees with me on this notion.)
At any rate, if today we stand not for The Crown, but rather for Handel and the wonder of his titanic genius, then I'm all for it. Let the tradition live on for another 250 years.