How can Ed Miliband criticise David Cameron for not getting support?

First things first, I am not a fan of David Cameron. I also don't entirely buy the whole EU veto triumph malarkey. 

However I do find it rich that the labour leader Ed Miliband can dare criticise Cameron's lack of support in the EU. Ed couldn't even win the support of his own MPs, MEPs, of party in order to become labour leader. The only way he became labour leader is because of the unions block votes. 

Ed couldn't win the argument in his own party and we are supposed to buy the spin that This very unimpressive man would win the argument in the EU by his eloquence and charisma. 

I don't think so!