Ooh, I don't like that idea so much. I could see a lot of reasons why that'd be a much greater risk than a cruise control you can turn on or off. Like in city driving.
I suppose it could be problem, but wouldn't you normally roll off the throttle anyway? I wouldn't just let go when I want to slow down. And it lessens the jerkiness on the throttle caused by the poor roads in my area.
And you can just roll the o-ring off of the grip flange with your thumb when you don't need it.
A built in electronic cruise control would have been a really nice option.