Even once disarmed, during WW2, this used to be a heated debate among those who were targeted by the Nazis; notably the Jews and all those sent to the ghettos prior to being sent to camps.
"There is more of us than them", "they can't kill all of us", etc... though true, it also relies on the premise that a portion of the population rising up against the oppressor will have to sacrifice itself for the greater good. Thing is, in a fight for survival, everybody is kind of fighting for his own personal survival and isn't going in as a willing sacrifice (that is, outside of very specific instances).
As Muck said, fear of reprisal played a huge role; however not reprisals themselves, but rather the scale of said reprisals. In and of itself, their persecution was a form a reprisal for merely existing, resisting would only make things worse. Yes, one can ask "how can there be anything worse than being sent to an extermination camp". Considering the outcome... okay... but in that case it isn't so much the outcome but how it is reached. In the end it goes down to the strength of the Human mind to see how much one is willing to endure.
So, considering theoretical and practical aspects, that debate is still open to conclusion, even in retrospect.
However, a point can be made that an armed population is "harder to oppress" than an unarmed one, but also that even in a case where the State has the monopoly on violence "those trusted to enforce laws and order won't do so if they are asked to enforce such laws and order on their own".
In the first case there would be the need to define what "oppress" is and means. From systemic, systematic and targeted attacks on a specific group of people to an hyperbolic "tsunami in a glass of water" scenario. There is real oppression (Nazi Germany, violent and repressive dictatorships, genocidal civil-wars) and then there perceived oppression (thinking about the trantifa and all of these women dressing as characters from the handmaid-tales). And though it is established the last ones are a minority, if a majority "felt oppressed" by whatever unpopular political decision and decided to go against said political apparatus, it would then end up being a mob-rule.
All is fine until you end up on the wrong side of the mob.
That's, perhaps, where I would disagree with Muck, in the sense I believe tyranny can go both ways and isn't just the appanage of the government. A government can be tyrannical, a leader can be tyrannical, a majority can be tyrannical and a minority can also be tyrannical.
The second case is something we see being brought forth quite a lot when it comes to the US, especially with regards to "the State coming to take out guns" or "your militia is no match for our military, you have rifles, we have F16". That argument, absurd and grotesque, is usually countered with "who do you think is manning the military? where do you think we live nextdoor to?"; implying "your militia" and "our military" are basically the same thing when considered down to the core: these groups are made of people who interact with one another, live close to one another, go to the same church, have kids going to the same schools, etc...
In other words relying on empathy and fear of a possible backlash to influence the moral compass of "the person in position of power, threatening to use their gun to enforce the established laws and order".
Thing is, and we keep on seeing this even today, some of these people are perfectly fine with "following orders", because they are indeed fine with said orders. Others could be reluctant, but the fact they are "following orders" means they did what they were supposed to do (don't question).
And then there are those who don't even need to be given orders. "Your honor, I didn't just follow orders, I also made a few of my own along the way."