Though we know that even if Gavin supported this fork and the network stays on mining the current fork, still there will be doubts among the general public seeing that one of the prominent figures in bitcoin leaves for another project.
The general public doesn't care. Hell, half the people in this community don't care beyond whether or not it will affect Bitcoin price. By necessity, the devs take a much longer term view of Bitcoin than most users and price is not - and should not be - their primary concern.
People leave projects all the time, often for projects similar to those they're leaving.
It seems to me that what people are worried about is that Bitcoin users will make the "wrong" decision and back the "wrong" horse. Maybe they will, but that possibility isn't a good reason to deny them the choice.