I think you're correct in saying that before a debate takes place, there should be a large number, like 10 MPs, sponsoring it. It makes me think that for a sort of less ambitious petition there should be an option for a member of Parliament to actually state online, “I have a duty to sponsor this because it comes from my constituents, but I disagree with this petition.”
On November 6th, 2014. See this statement in context.