Now that I think about it, you're probably right. If Microsoft could ensure that there would be no second-hand market for games, publishers may have been more apt to accept the family-sharing plan.
Maybe.
Their reasoning for why used games are bad is that if someone buys a used game, they wouldn't buy it new. But how many owners do you think a used , physical game goes through? Probably not more than 2, or 3. Mostly 1.
Say someone sells 500 copies of a game. 20 people sell it, and 20 people proceed to buy it. 10 keeps the game, and 10 of those then sell it again, and 10 people buy it again. 5 of those then sell it again, and 5 people buy it. That's 35 lost sales.
Now, assume that they sell 500 digital titles, and 20 people share it with 10 friends on an online service. That's 200 lost sales. Not to mention the fact that there'd instantly pop up "groups" all over the place to take advantage of this service; if you could simply friend someone and play up to 10 games for free, that would result in far, far, far more people not buying games. Also, these titles could be easily shared at any time -- they'd very accessible for everyone. Used games on disc availability depends on someone selling it at a store. I think a lot more people would buy used games if they *knew* they could get a hold of it on launch day, or if they were easily accessible -- which seems to be what this service was supposed to do..
But how would the refreshing of games work? If someone has 20 games, could they replace the games on their shared list at any time or once a month or something? If you could simply friend someone that buys every game, there'd probably be tons of people who wouldn't buy any games anymore - if they have legal access to every game, what's the point of buying except for collecting? Which is almost irrelevant with digital titles. Or, you know, you could just join several groups that do not change their shared titles, and some that do update with the newest; that's basically as good as a digital collection.