I like the idea that one person can veto an idea. After all, this is something we're all supposed to be happy with, so if something annoys someone enough they should be able to get rid of it.
However, I also think vetoing shouldn't be free. Here's how I'd do it: A veto costs 2 points. The person who pitched the idea loses his 2 points. Anyone who supported the idea gets their points back. This also applies to "silent" vetoes; the pitcher still loses the points, but if one person supported it he should get his points back.
Net result is that each pitch takes 4 points out of the system regardless of whether it's vetoed or not (except in the case that it's killed by a silent veto), which makes the duration of the game a bit more predictable.