My guess is this is probably some fresh faced national guard n00b who thought "Hey, buzzing this Cessna should be hilarious".
This is an ignorant thing to say. Maybe you didn't mean it out of malice but it shows a profound lack of knowledge of both military and general aviation.
I've been flying for about 27 years now. In that time I've had about 5 "near midairs", a few while flying cessnas and a few flying military aircraft. "See and avoid" is the responsibility for everyone involved, however its ironic that as others have already said, the hardest aircraft to see is the one you're about to collide with. This is because there is no apparent motion, or "line of sight", to catch your attention. An aircraft on a collision course initially looks like a motionless dot. It slowly grows bigger and if you're not staring at it, the time from when it becomes more than just a dot to when it is obviously another aircraft may be mere seconds and you'll miss it. Visual scanning techniques to combat this problem can be taught but they take practice and discipline to master and use effectively. And even then, sometimes the most intense visual scan isn't enough. Sometimes the other aircraft is masked by environmental conditions like sun angle or haze, sometimes a canopy frame or wing is hiding the other plane.
Stating that a midair must obviously be the fault of a careless military pilot is really pretty ignorant and insulting. An awful lot of people would take grave offense, but I'm going to assume that you just don't know any better.
My first near-midair came when I was a 35 hour student pilot, just buzzing around southern California in a Cessna 150 building hours and experience. I went nose to nose with an old A-7 corsair who had his landing gear down and was flying in uncontrolled airspace much lower than I ever expected a military jet to be. In hindsight, I think he was probably getting vectors to a long instrument final to NAS Miramar since I was probably 15-20nm east of Miramar and within a few miles of the extended runway centerline. He must have been at absolute minimum vectoring altitude due to the mountains we were flying over, and he must have been getting very extended vectors for him to be so far out with his gear already down. I was slightly lower than him, so he probably never saw me through the somewhat restricted low-fwd view of most naval fighters due to radomes and thick canopy frames. For my part, I was sightseeing and saw him just in time to think WTF as he flew by within about 100 ft, nose to nose, slightly higher and off my left wing. Fault? Nobody except maybe an overworked radar approach controller who vectored this guy into a student training corridor at a fairly typical Cessna sightseeing altitude. I was squawking VFR but "not participating" so legally the controller may not have been required to provide separation, but that navy pilot was for damn sure relying on the approach controller to keep him separated from other traffic since he was likely heads-down flying on instruments. Thing is, even on an IFR clearance and shooting an instrument approach, if you're in VFR/VMC conditions then all pilots are still required to maintain a visual lookout.
So as for fault... I suppose that'll come out in an investigation. But if they were in VMC conditions and one or both was not participating in an IFR controlled environment, then its really both their responsibility. If they were in a published low-level route, then the unlucky civilian pilot either didn't plan his route very well or he tried his luck flying through a military training area one too many times. I always thought GA pilots who flew through high volume MOAs were idiots, same goes for GA pilots who like to hang out in published military training low level routes. It may not be illegal, but they're taking their lives into their own hands when they do so and placing blame on the other guy doesn't make them any less dead.
That was always one of my biggest challenges as a UPT instructor... Keeping high enough SA so I could both monitor what my student was doing and still keep up my visual lookout. I can't count the number of times I had to take the controls to abort some training or aerobatic maneuver because a GA aircraft wandered through our training area. They have every right to be there, but they're taking a bigger gamble than most realize when they ignore widely published warnings about high volume military student training. We had a midair near Sheppard several years ago between a T-37 and a cropduster, up at around 7000'. The cropduster was transiting through a high volume transit route between Sheppard and our auxiliary field in Frederick OK without a radio or transponder. The instructor pilot was probably busy instructing his student, and they collided. Military guys survived due to ejection seats and parachutes, cropduster pilot died. Both were "legally" in the right, both had the responsibility to see and avoid. The military guys were in the middle of a known high-volume student corridor, the cropduster was right there too with no radio contact and no transponder. Who has the greater responsibility for what happened, the guys predictably doing what they were supposed to do, or the guy in an unexpected place taking no precautions against what ultimately happened? It doesn't matter, the cropduster pilot died doing something perfectly legal and it could reasonably be summed up as a failure to see and avoid in VFR flight without placing blame either way.
