QUOTE (Lolly @ Oct 9 2013, 03:20 PM)
Who? And is changing political party abandoning your principles, or making a principled decision?
It rather depends.
Changing party because your politics is sufficiently at adds with that of the party you once joined isn't especially principled, it's just obvious. It would simply be perverse to be a member of a political party whose politics you didn't agree with.
Leaving a party over a single issue when you otherwise agree with the party's politics might reasonably be described as a principled decision, especially if you leave behind the personal and social benefits of party membership.
However, moving from one party to another because your political ambition is likely better served in the other party is pretty shallow and unprincipled.