Although I agree with what is being asked for, frankly, what is the point?
I would sign if I thought that there was one.
Every political issue which involves a previous Labour "decision" (or as in this story - involving common decency or sense from one of their own) when put to the No 10 site results in a response which boils down to a patronising
"Thanks for your opinion. We have ours too and your petition isn't going to change it. Now F off......"
The site is simply there to act as a sop to any activists - it allows them to think they are making a difference when on results, they are anything but.