We know exactly what it is and does:
It's an intrusive digital distribution system that restricts our consumer rights. It eliminates our resale rights (should we choose to want them). It forces us to be reliant and have ongoing relations with a third party in order to use our product. It forces us to maintain an Internet connection perpetually in order to use the product (heaven forbid hardships might have us consider canceling the service). It maliciously transforms software from a "buy and get" state to a "rent for a long time" mode.
OK
1) Ya it does take away resale
2) There is no relationship between companies needed to have games on steam, even if something weird happened like 2K decided to buy out valve or they didnt get along or whatever. Nothing would happen. Valve gets money from the deal and 2K gets their game sold, both parties win.
3) No it doesnt require internet service
4) It is still buy and get, in fact its better. If you install steam on any computer and then log onto your account you have all your games automatically. If you decide to uninstall a game it stays on your games list so waiting for you to decide to reinstall it. Steam eliminates the risk of losing your disk
(Something much more likely to happen than one of the biggest and most respected companys in the industry getting shut down or getting bought out)