Starting a petition with a view to getting a sentence changed amounts to requiring, at the very least, public input into sentencing decisions. And that's very dangerous. There are loads of sentencing decisions made every day in every court throughout the country, some of those decisions will by their nature be wrong, but no-one puts up public petitions about them. Why should the media decide which ones it will publicise so as to whip up public disquiet, and which ones they will leave alone?
Of course people can have an opinion, but I don't think there is any point in signing a petition about this particular sentence because it won't achieve anything as the Attorney General has no power to review it in any meaningful sense. Plus, as I say, petitions directed at individual sentences seem to me dangerous. I'm not criticising anyone for their opinions - after all, I've said above that I don't think this sentence is fine.
And why don't you start a petition to suggest sentences by revised to reflect justice in that case?
Why don't you? Genuine question: if you're outraged by the sentence in this case, aren't you equally outraged by the similar sentences passed in similar cases?