There's nothing wrong with wanting to know what one would be voting for. Labour's policy is not a binary option and is predicated on the notion that it will renegotiate with the EU and offer a second referendum. If the British people dislike that deal, then we will be out.
What is unclear about the policy? If voters want a binary choice, then by all means I would suggest that they vote for a different party which has a binary stance such as the Lib Dems or Conservatives, but to suggest that it is not a clear policy would be to misinterpret the rules of the English language.
I'm not convinced this is true, as Corbyn himself has long been a Eurosceptic. Sure, a large proportion of the rank and file will be Remainers but this does not translate to a Remain policy - or else they would have committed to it. Why would they risk losing votes to the Lib Dems/other progressives when they could easily posit themselves as the only realistic hope of a benign Brexit/no Brexit at all?