Advertising (including targeted advertising) is not election tampering. It's how elections work. This stuff is obviously the future of any kind of mass communication campaigns, and is an obvious extension of past work. It was a significant part of the Obama strategy in '08 (also Ted Cruz, although less successfully).

None of that means you have to like it, but it does mean that the focus on Facebook is counter-productive. They're definitely not the only party pursuing or interested in this. A big public backlash can probably trash their stock for a while, but it won't change the direction that politics is going. That's going to require policy changes, if it even turns out to be a good idea.