It's actually a somewhat rational position for Labour MPs to hold. Brexit is a Tory project, organized as a Tory way to resolve internal party conflict. The referendum was proposed and legislated for by a Tory governing majority, article 50 was invoked by a Tory PM and if there is a no deal Brexit it will be a Tory government overseeing the disaster.
Much like Trump, the no deal Brexit has the potential to soil the Tory brand for time immemorial, relegating them to a minor local party and banishing them from national politics forever. The new opposition from the right will come from a group splintering off the useless, corrupt remainder of what was once "the natural party of government".
If you accept the potential the potential to rule the country as the undisputed ruling party for a generation as large enough to be worth whatever damage the no deal Brexit crisis will bring then sabotaging any resolution to the issue is a rational position. Yes, it is corruption that is worth a firing squad or worse (HD'n'Q?), yes, it is horrible, but the position itself may well be rational. Until you vote against your party whip anyway.
Tory MPs? Beats me. Maybe they just really, really, really want to change careers but don't want to quit or something.
McHrozni