Kevin,

You cannot hijack someting that is already yours. This is the spirit of open source. When you release a piece of code under GPL license, as SugarCRM did, you are authorizing other people to use, transform, develop, work with, or improve your piece of software.
If you are not prepared to see how other people take advantage of your code, just don't play the game.
SugarCRM decided to play the game, and there was a community of enthusiasts that helped SugarCRM to create a better application.
vTiger took the sugar open code, and created something that has more features and is open code too. That is the same process that has led linux to grownt into a fine piece of art.
It is a pity, but Sugar has decided turn their back to the open source. I envision what a beautiful piece of software could have been created between both Sugar and vTiger if they had joined forces.

Jose.