Yes, charging tanks with horses is stupid. However, you might also look to Finland and the USSR, in the Winter War. Guerilla actions by an outnumbered and vastly outequipped Finn defense (32 tanks vs 6500) absolutely devastated the Russians, with a 5 to 1 casualty ratio. Furthermore, an armed populace turns every house, every apartment, every church and every office building into a potential sniper nest. Every road into a potential minefield, every alley into a potential ambush.
Many "pea shooters" owned by the US Citizenry already (and legally) are more powerful than US Army standard issue. But you're missing the point - it's not to say that an armed citizenry can go toe to toe with a trained military and win, that'd be stupid - why even have a military if that were the case? No, what an armed citizenry can do is make it more costly in men, materiel, and political will to occupy/suppress a population than the occupiers are willing to spend. After all, it's how we got run out of Iraq, handing it back to a re-branded Al Qaeda.