I still am unsure as to why MP's are angry.
Oh.... lots of reasons and you did a good list but there's one more...
There's the implication and apparent evidence that Cambridge Analytics interfered big time in the US election. If they held data from FB's British users, there could be worries about your elections being tampered with from them. FB might not have a hand in election tampering but the data leak could certainly be shown, if used by a firm like CA, to sway an election.
There might be a connection between all this and your elections.... for example Brexit.
FTR, we should all be pissed about data theft, be it from FB, any business, and/or government. Yet, most people aren't unless it affects them personally, like the resulting bank fraud or screwing up their credit.