Principle or pragmatism. The false dichotomy of new labour

Why do you found a political party? Is it simply to get power? No, if that was the reason you'd join an existing party to use as a platform. At best you'd try to influence it 'from within'.

No, you found a political party to campaign and argue for ideals in which you believe that aren't being represented by existing parties. The idea that public opinion is unchanging and unchangeable, and political parties have to manoeuvre round it, is bizarre. It's worth noting that the Tories certainly don't believe this - but it suits them that so much of Labour does.