The US is a representative, constitutional democracy and a federalist republic. What does government oppression (aka tyranny) look like in such a government?
Gun-rights activists love to claim that they're members of the unorganized militia until you point out to them that the Constitution doesn't make any distinction between the organized and unorganized militia and that Article I, Section 8 explicitly grants Congress the right to organize, arm, and discipline the militia.
Amending the Second Amendment would take overwhelming public support
Amending the Constitution is intentionally difficult, requiring 2/3rds of the House and Senate to pass an amendment and ¾ of the states to ratify it. Amending the Second Amendment would require an overwhelming supermajority of Americans and a tectonic shift in public opinion about guns.