I am not so sure.
Consider our Westminster MPs. You would have thought that they would have not supported the EU as this diminishes their own powers - however - support it they do!Clearly, that explanation is laughable.
Ergo, one can only conclude that it is either crass stupidity or a 'lemming mentality' which guides them.
In Brussels how good to see the UKIP MEPs trying to put themselves out of a job. Now that really IS 'principle'.