Defections happen all the time in politics. Of course, the more high-profile the person defecting, the more newsworthy the event. The defection of an MP is big news, the defection of a sitting Councillor or parliamenary candidate less so.
ANY defection to the Conservatives is treated as a major news event by the pro-Tory media and the defection of the Lib Dem PPC in Chelsea & Fulham is of special significance.
Now, I don't quite understand why Ms Bhatti has decided to jump so publically. David Cameron may call himself a "liberal conservative" (whatever that means) but while some may be seduced by his words and the prospect of power it's a big step to simply switch parties.
If you talk to most activists, you soon find they have little time for defectors. Winston Churchill of course ratted and then re-ratted but he was unique. I would contend most defections are for reasons of personality differences than matters of principle. I've seen Council groups of all parties implode because individuals became unable to work with each other or together.
I think others defect for reasons of personal advancement. At the moment, if you're ambitious, the Conservative Party is the place to be. Simply pay lip service to the policies and you could be on the ladder to real power and influence. That may be overly cynical but for those seeking to be close to power, it's the obvious route. Perhaps that's the thing about politics - power attracts not only the principled but also the unprincipled.
For my part, I've not always agreed with everything the Liberal Democrats have said or done. I think Nick Clegg got the Lisbon Referendum badly wrong but I've never seriously considered defecting in my 30 years of Party membership. I suspect for me, disenchantment would lead to withdrawal rather than defection but that's just me.