But keep government in check?

I don't see regular people having RPG's and the such

How are regular people going to stop the government from rolling tanks and helicopters down the streets

I just don't understand, if the government wanted to, military would overpower society very easily even if society has guns

So if you can't win why bother fighting? That's a bullshit argument to deny people needing guns to fight against the government, some people (the ones who'd fight back regardless of the odds) would rather die than give up their freedoms willingly.

I just don't understand, if the government wanted to, military would overpower society very easily even if society has guns

No, they really couldn't. You need soldiers, actual flesh and blood humans to keep any kind of control over an area. You can't keep people from congregating on a street corner with a jet flying a mile up in the sky. There are over 75 million gun owners in the US. There are just 3 million soldiers in our entire military, most of them aren't even infantry. That's one soldier per 25 known armed citizens or one for every 100 citizens total. If enough fought back, they would never win.

“The supreme power in America cannot enforce unjust laws by the sword; because the whole body of the people are armed, and constitute a force superior to any bands of regular troops that can be, on any pretense, raised in the United States.” 
– Noah Webster, “An Examination into the Leading Principles of the Federal Constitution (1787)

The military is made to protect the constitution not the government itself. Yes there will be some that will fight for the government but a vast majority will not fight for the government.

Seems like a legitimate reason to me, even though countries like Germany, France, Denmark etc. don't need guns, in order to "keep the government in check".
But it's a fair reason, I see!