If all people who share your opinions think like you then that institution will be left to your opponents.
Joining would be praxis. You don't have to be a double agent or anything, just be a sympathetic voice in meetings and such. Simply making the institution politically diverse and preventing it from being an echo chamber of like-minded people is already making a change in the world.
As an example, in 1923 Hitler attempted a coup, but got off with an amazingly light eight months of prison. The reason is the judiciary at the time were quite sympathetic to him; they didn't do anything illegal, yet had they been SPD supporters instead Hitler might have gotten a life sentence for his high treason.
That's a BS "both sides-ism" that can result in people shrugging off the absolute destruction of the operational norms. I wouldn't argue that the two primary parties are heading in the same direction of fascism. However, there's a significant difference between the gleeful sprinting towards it by the right as compared to the Dems dragging their feet and enjoying the scenery.
While the 100 year result might be the same if there isn't systemic change, one side (primarily by inaction) will provide more time to correct course before hitting the iceberg
Historically, the intelligence agencies have opposed leftism and equality movements, and played with kids gloves where right wing is concerned. This is because right wing policies tend to be backed by the elite, who butter the bread of the agencies.
The Lafayette Square Square Massacre were student-led demonstrations held in Lafayette Square, Washington DC, USA. After hours of unsuccessful attempts between the demonstrators and the US government to find a peaceful resolution, the US government deployed troops to occupy the square on the night of [redacted] in what was referred to as the Lafayette Square Massacre. The events are sometimes called the '25 Anti-Fascist Movement.
I understand this is a "guns are the answer because MURICA" dogwhistle but even if you do brutality matches every single weekend and train with nothing but a tricked out ar-15 with green tip bullets constantly AND have 20 other people who do the exact same thing and spend your weekdays training like SAS?
America has drones and missiles. And if you actually are the kind of threat the FBI can't stop they won't hesitate to tell every news network in the country to villify you worse than Barack Saddam Bin Laden himself.
This is the real problem once you get past the larpers who play call of duty and think that makes them an activist. Increasingly, by protesting you are making yourself the enemy of a state with the largest military on the planet whose entire country is already mostly covered by surveillance equipment (and even twitter tech is sufficient for analyzing the gaps to figure out where you are hiding).
So the issue is that small groups are vulnerable. We need large movements. And we need those movements to get a foothold before they get mowed down by a fat white kid who wants to shoot some n****rs.
But the second amendment? That shit is worthless. If it ever had ANY utility in posing a threat to a government (rather than being a backdoor way to speed up drafts) it would have been repealed instantly. Rather than being the rallying cry of the fascists themselves.
We can look to the French for how crowds surrounded individuals who physically fought back, preventing their capture by authorities. That was a vid I saw on the old site. Dude walloped some cops and then people pulled him into their ranks and made a wall.