I will stress the point yet again:
The militia does not fail because of guns. A civilian militia can have the most advanced guns available in the world, which is what you're suggesting. It's not about the guns. It's the fact that guns alone will not win you a war with the US government. You need tanks, air superiority, and naval forces to stand a snowball's chance in hell. And it's about training, because it will take months to year(s) to get your people ready to use such equipment and not have them accidentally kill themselves. That is why your militia will fail. The traditional militia you are thinking of is outdated and ineffective, just as it was in the era of muskets and cloth jackets. A nation that has routine conscription, however, is a more "modern" militia that stands a vague chance.
If you're serious about your argument (making sure civilians can overthrow the government), you should be just as worried about training and the whole scope of the war. Conscription of all 18 year olds in good health should be just as important to you as the guns, because professional training is the only way to keep the citizens of America ready for just such an emergency. A traditional militia is almost certainly doomed to fail. So what is the case? If you really want people to be able to overthrow their government, you should be for conscription or formal training of some kind. Otherwise it mostly seems like an excuse to keep high powered weapons in your home. Because like I said: Just having a gun doesn't mean anything in a real war if you don't have the training and a well rounded army. Just handing someone a rifle isn't being serious or at all realistic.
However, the argument for gun ownership in the event of a zombie apocalypse is still quite strong.
Still, if I had my way, I'd limit gun ownership to hunting and basic self defense. But preferably tasers or other non-lethal close range weapons for self defense. A gun is only really effective if you have enough time to get it and load it before you're attacked. Which, if you're caught off guard (as is the case with murder attempts and many break ins), is not terribly likely. I keep a knife by my bed instead of a gun. Less time needed to get ready, less noisy, no ammo, easier to conceal, and still quite deadly. Sure, guns might be left to the 'evildoers' of society in this scenario, but if they get their gun trained on you before you can get to any of your weapons, having a gun of your own doesn't matter. You're screwed either way.
If things are going south, who's to say that people wont start training? If I felt that the government was going the wrong way I would go out and join up with an established militia for training. Hell, even now we have PMCs (even though they aren't used for that purpose) and that industry is growing and has currently reached a worth of 100 billion a year. But, all the training in the world will not matter unless you have weapons.
If you're using a gun for self-defense you keep it loaded with the safety on. Yes, but (by your argument) if that person has a bat, you're screwed, if that person has anything with a longer reach than your knife, you're screwed, if that person has a gun, you are most screwed. Therefore we should ban all use of knives in the terms of self defense, except under strict regulation, because they are useless and outdated and sure, they might be left to the "evildoers" of society but if they knife you before you can get to your knife, having a knife of your own doesn't matter. You're screwed either way.