Re: Who to choose?
Labours core vote (the working poor) was the bit of the country voting most heavily in favour of Brexit. If Labour turned around and said that they are going to block Brexit if they get elected then Labour would be utterly annihilated as their core vote decides to sit at home watching TV instead of turning out to vote.
Therefore, any Labour leader with a shred of intelligence would not make such a commitment.
Of course, if Labour doesn't make that commitment then the self described intellectuals who don't have the intellect to come to this conclusion themselves will vote for the lib dems, which simply splits the vote and clears the way for a Conservative victory of historic proportions, at which point those same "intellectuals" will then turn on the labour leader like a pack of rapid dogs for losing the election.
Hence why May is going for the election now, where she also stands to gain the UKIP vote back.