No-one thinks it impedes free will problematically when humans -- e.g. the police -- prevent acts of intentional evil. Why would it be any worse for God to do the exact same thing?
It doesn't seem that the mere source (human or divine) of an obstruction should make any difference to whether it impedes the criminal's free will. In response, Brandon acknowledged as much, but pointed the issue in a new direction:
[The FWD] can't work on individual autonomy alone; rather, it requires us to say that not only is individual autonomy a good to be valued, but the autonomy of the human race as a whole is a good to be valued.
Is it, though? Is collective self-determination or 'sovereignty' an intrinsic good so important that it could outweigh all the other goods that could result from the perfect enforcement of individual human rights? At the level of the nation, most of us think not. Indeed, we think it morally incumbent upon outside powers to step in to prevent genocide when they are able, to protect innocent individuals -- even those with the misfortune of living in the wrong 'sovereign' nation, under the wrong rulers. (Humanitarian intervention may be questioned on pragmatic grounds, of course. We're not omniscient, so the interference of fallible human actors may do more harm than good. But the principle seems clear enough.) Is there a difference at the level of the human species as a whole? Brandon offers the following thought experiment:
A powerful and very advanced alien species comes to Earth and begins intervening in human affairs, not by interacting with us as equals, but by, effectively, policing us. Even granted that the policing was entirely benevolent and beneficial, I think a great many people would feel, perhaps in virtue of a fellow-feeling with other humans that they don't share with non-humans, that something precious to human life had been exchanged for that benefit. Some, no doubt, would think the exchange worth it; some would forcefully reject it. I suppose how people would react in general would tend to depend on the precise details of the interference. But, regardless of how exactly the demographics would go, I think the scenario does suggest that we tend to assume that human affairs are human affairs, to be determined by human choices. And that suggests that, to the degree we treat the whole human race as an object of value, we treat as valuable the autonomy of the human race as a whole.
Again, as in the standard humanitarian intervention case, I would be worried on pragmatic (indirect utilitarian) grounds. Alien or foreign powers are not generally known for being 'entirely benevolent and beneficial'. So in practice we should be suspicious, and a preference for self-determination may be for the best. But if we may stipulate that the outcomes here are, in fact, most beneficial for people, then that strikes me as a very desirable state of affairs. I would rather have a perfect police force than a local police force. Wouldn't you?