Then and now, the 2nd amendment was a contentious issue. Different people and groups pushed for it and they gave different reasons.
One, not mentioned, was historical. Under Feudalism, serfs could not bear arms (meaning knives or swords). That was a right reserved to the free-born. In an era when slavery still existed, even in the North, free-born was an important and meaningful distinction.
Related to this, many people fear slave rebellions and wanted the right to bear arms for protection from slaves and to keep slaves in their place.
There was the issue of posses being able to pursue criminals (as de facto militias).
And, of course, some people feared a strong central government and wanted arms and militias as protection from federal "tyranny." Remember, the colonies first adopted the Articles of Confederation because they did not want a strong central government. They fought a war to get rid of one. They just got finished fighting off a regular army with self-armed militias. Each colony were fighting for its own independence, in alliance with other colonies doing the same. At least that's how they saw it at the time.
It was a different time and a different world. The 2nd amendment, like the other original nine, was a reaction to things that had just happened to those people, things they feared could happen again.