I dunno about uncovered "being a bad idea". I mean yeah, in a perfect world we would all have 100%-predatorproof runs and all that, but there are some real tradeoffs involved here for many people.
First, a large run is going to be difficult-to-impossible to put a top on, especially if you have trees in it. But in a lot of ways I think chickens are better off with a really large run, even if there is some hawk threat, than in a very small but very secure run. (Both sides can be debated, I mean, but, the point is, both sides of the argument DO have merit)
Second, if you have trees in your run, that *in itself* is *some* protection vs hawks. It certainly ain't perfect but basically your chickens are going to be a lot less visible to hawks that happen to be drifting past, and there are generally fewer attacks.
Third, if you want to use some kind of netting, you have to decide about the economics. Even just deer or trellis netting is not entirely trivial in cost; and you may have to end up replacing it *repeatedly* if Mr Raccoon and Opossum start breaking in regularly (at the very least, keep your feeder INSIDE the coop!). OTOH serious aviary netting is expensive. And any of it can get taken down by falling limbs and snowstorms. I do not think there is any one right answer, it depends on what you want and what you can afford.
Good luck, have fun,
Pat