As far as the ATV stuff goes, here's what I THINK I know
Every deer has a personality of its own. What bugs one may not bother another, and I'm quite sure this applies to ATV use, as well.
When ATV use is consistent, as in at least several times a week, preferably daily, taking the same routes over and over again, at least the majority of deer don't care. They become trained to pay almost no attention at all. I could bore you with a bunch of stories about an outfitter that drove every client directly to the tree (but also drove all over his place nearly every day of off season) and a different piece of ground I managed that had an active oil lease on it with the maintenance guys driving all over the place 6 days a week, year round. In both cases, the overwhelming majority of deer wouldn't leave a food plot with an ATV driving 20 yards away. Some of them wouldn't even raise their heads.
On the flip side, that same piece that had the active oil lease, the guys running it got their hands slapped by the DNR (or whoever it is that enforces the oil regs) so hard that they couldn't justify all the clean up work they'd have to do to get things back up to code and stopped their oil operation cold. Within months of that happening, a good % of the deer would run from ATVs, as it was no longer a daily part of their lives.
I don't believe ATVs are as bad as many believe, but I sure don't think they're harmless in MOST situations either, unless it's very consistent use.
That said, I also try to remember that this stuff is also supposed to be fun. Let's face reality here. Many of us that head out into the deer woods are in horrifically bad shape. If you make them walk up that ridge, 25% are going to have a heart attack before getting 10% up and the rest will be a sweaty, gasping mess that are praying for death by the 50% mark. That's NOT going to be "fun" for them. I try to take that into consideration for those clients and the hunters I have on the grounds I manage that are in less than marginal shape.