Well, the purpose of social media is to share and display. In that context, the Google+ license is actually quite acceptable. If you invert your highlighting, you have one of the most benevolent license available right now in the framework of social media. For photographers, sharing low res versions of files is essentially risk free. It should also be noted that this license applies to Gmail as well: if you fear Google will steal your picture, you must also fear they could possibly read your mails and share them with the world, or steal your next novel if you happen to be writing in in Google Docs. Given Google's business model, petty theft is unlikely to happen as the consequences for their bottom line would be too significant.
If you don't want that risk, run your own boxes, servers, their security, etc... etc...
Of course, a picture gets stolen from time to time, usually not by public entities that have a lot to lose in terms of reputation or eventually assets. But that's what happens with cell phones, cars, jewels, ideas, articles, root certificates, etc...
Do we know of a large scale systematic covert photographic asset grab and use by some similar social/hosting service? (genuine question, I haven't looked into this...) I was under the impression that large agencies whose open purpose is to showcase and sell the photographer's work did a lot more damage when they unilaterally changed terms and users were trapped, not necessarily by legale, but by practical issues.
Anyway, I don't share a lot either and run a lot of what I need in-house. But being on social networks is a bit like driving - they are risks, drunk people, thieves, etc... but you can statistically survive through all that by driving carefully and using common sense.