The Victorians (at least, those in the Palliser novels) had the maxim for these situations, "Men not measures". Meaning that you should vote for the person you want as your MP, not their party or manifesto.

If you elect a reasonable person as an MP he or (now we're not quite so Victorian, thank goodness) she may well change their mind towards more reasonable policies. But if you elect a knob you're stuck with a knob.