It's security of a FREE state. In order to keep a state free, the government and the police officers by extension need to be scared of an armed populace so they don't enforce tyranny.
If I dislike a policy by the state a little bit, the state isn't going to be gunned down over it. For instance, if taxes are raised by 10% among every income group to pay off the debt, people probably won't LIKE that, but it's not enough to start a revolution. It's only when the government does something absolutely HORRIBLE that is despised by huge portions of the population that the government is going to have to be scared people using their 2nd amendment.
The 2nd amendment won't prevent the government from doing something that is merely a little bit bad. For example, my state abolished the death penalty for murder. I disagree with this, but it isn't something so horrible that I start a revolution over it. The 2nd amendment is designed to prevent the government from doing something absolutely Horrible and it forces the government to come to a consensus not strongly despised by too many people within the place they are governing in order to prevent a revolution (by building consensus).
A country without gun rights can have a government that doesn't depend on consensus to get laws passed. Such a country can rely on one party rule and minor parties don't get much done. This is how California (a place where semi-automatic guns are banned) is able to achieve reliable one-party rule by locking down their entire state, and the citizens can't challenge the government because if every republican and every independent voted for the republican nominee, the democrat nominee would still win. Gavin Newsom can pass almost any piece of left wing legislation (no matter how radical) and the Californian populace can't do anything about it because they banned semi automatic guns. If Greg Abbott wanted to do something like significently restrict abortion, since Texas is way more gun friendly, democrat gun owners can protest with semi automatic guns to scare the government into giving people liberty.
But even Texan liberal women don't want to arm themselves, so Texas is going to become anti Roe V Wade and there is nothing that will happen because of it because the left is too cowardly to arm themselves.