labour aren't interested in making Brexit a party political issue, rather their intent is to wreck whatever the government field - irrespective of the content - in the expectation that it will precipitate a general election. if labour were to win, they are unlikely to do any better with Brexit, their party is just as divided as the tories, the difference being they don't have to (yet) pretend to be united. Keir Starmer might advocate remain but the leader is still JC and he's a Eurosceptic, and his (and momentum's) renationalisation programme cannot be enacted as envisaged with the UK in the EU.