Why should it get touchy? Because of the crowd that always shows up with the "its my RIGHT to fly through a MOA!!!". What they don't realize is that thats not the question at hand. The question should be simply some common sense applied by aircraft that aren't participating in the MOA. Remember, there's a difference between "I CAN fly through there" versus "Should I fly through there?" It's never an all or nothing answer though. As usual, it depends.
First off, flight planning. Know where you're going and whats on your route. Know what MOAs or MTRs are around there (MTRs for low level). Second, check the NOTAMS. If the particular MOA or MTR isn't active that day or time you're going to head through, then the hazard potential is vastly lowered. Third, if it is active, go to a Sectional to where the MOA list is, and find out what the dimensions of the MOA are. For all you know, it may not go to the surface or even near it, so by flying under it you won't even be going through it anyway. If you HAVE to go through it during a time its active, know that you NEED to be on your toes see-and-avoid wise, as the traffic you'll likely encounter won't be your normal everyday traffic coming at you from straight and level.
In short, do some homework on the ground prior to just tooling through one of these SUAs.
Years ago, I was flying a low level along VR-239 north of PHX. Cruising at 480 KIAS and 300-500 AGL, I was doing the standard clock/map/ground as I navigated along and around the terrain on the route. Coming around turn point 4, I happened to spot, by luck, a Cessna 177 doing what appeared to be turns on/around a point at low level.....standard training. Glad I spotted him earlier, and no problem making a deviation around him, but had I not spotted him, it could've been a close call or worse. He was likely concentrating on his airwork, as I was mainly concentrating on map/ground, so it's even more luck that one of us spotted the other. I don't know if he ever saw me, but I doubt it, since I was at his 6-7 o'clock when I first spotted him, and lagged around his six to pass him by a good margin as he completed his left turn.
IMO, practicing airwork in a MOA or along a known MTR, anything where training is going on and full attention can't be maintained to the outside, is potential trouble waiting to happen IF one doesn't do their homework as I mentioned above.
Military Training Routes are usually never in "military-only areas" such as Restricted Areas, etc. As military pilots, we train like we fight; and if that means a 450 knot low-level ingress to a target, then that's what we do. There's a reason that MTRs in the USA are depicted on Sectional Aeronautical Charts and the US AP-1/B chart; that's so civilian pilots can plan around them, and either avoid them, or be able to be VERY heads-up if they must fly near them. When I say "must fly near them", I'm referring to some MTRs which come within (due to terrain) some small private, uncontrolled airstrips, such as those near ranches, etc. In these instances, civilians need to go in/out of these fields, and knowing the status of a particular MTR near you is important.
It's perfectly legal to fly through/in MOAs and along MTRs, but as I mentioned before, that's not the question. As you know, in VMC, it's everyone's responsibility to see and avoid. The question is, once you've done your homework and found out that the particular SUA is active, is is it smart or prudent to head through it if unable to avoid? And, can everybody see and avoid?
Here's a good example of the problem from my end as a military pilot, insofar as my ability and limitations to seeing and avoiding: In the A-10, I had no radar for my low-levels, my only separation ability comes from the Mk.1 eyeball. Keep in mind, though, that I have a multitude of cockpit tasks going on while tooling along at 300 AGL/360 KIAS. First, eyeing terrain to make sure I'm doing my job of pilotage correctly (ie- matching terrain features with what's on my map to make sure I'm going the right way), avoiding hitting the ground/power lines/near rocks/far rocks, keeping track of my timing per leg [if I'm going for a specific TOT, or Time Over Target], keeping track of my other aircraft in my formation, insuring my weapons panel is set correctly [such as setup change from air-air to air-ground], going over and over in my mind what the attack plan is [formation, role, weapon, timing, attack axis], and being ready to flex to a different plan if the first one gets screwed up [such as unplanned threats pop-up], and maintaining overall SA over the operation; all while moving at 300 AGL/360 KIAS; and all this in addition to trying to see and avoid. Truth be told, we really expect (hope) that civilian pilots won't be in our path because they HAVE done the necessary pre-planning for their flights. Even in radar equipped fighters, the pilot isn't sitting with his head in his scope while tooling along at low level, so he may not notice civilian hits on his scope. In addition, some radars are even programmed to negate hits below certain airspeeds, in order to reduce the scope clutter. Also, at the speeds mentioned, I'm moving @6 miles/minute (A-10), or 8-9 miles/minute (other fighters); a Cessna 152 would probable be visibly detectable for only a couple of seconds before I flashed past it. Point? Everyone practice the best see-and-avoid they can; but also civilian pilots should be aware of where Military Training Routes are and, preferably, avoid them. Military pilots should know what their route structure is, and remain within it.
So contrary to popular belief, the biggest onus for midair collision avoidance in a MOA or MTR isn't going to be the participants, it's going to be the non-participating civilian plane cruising through fat/dumb/happy. And thats not talking legally, its talking realistically. Plan accordingly.