You're doing what you're complaining about - selectively interpreting it to mean what you've previously decided you want it to mean. Despite the fact that what you want it to mean is very clearly not what it actually says. You might quote it but you don't understand it. Or maybe you do but hope other people won't and will take your word for it.
Commas are not merely randomly placed decoration. They have a significant meaning. As an example, consider these two sentences:
I like eating, dogs and my neighbours.
I like eating dogs and my neighbours.
The words are identical but the comma radically changes the meaning of the sentence.
In the case of the second amendment of the USA, the meaning is that the right of the people to keep and bear arms shall not be infringed. The bit about a militia is a supporting argument for that and a clarification of the type of arms being referred to, not the core of the meaning. It could be left out entirely without changing the meaning of the amendment.
It wasn't written that long ago. There is plenty of extant evidence for what the amendment means (taking into account the usage of American English at the time) and what the people who wrote it and the people who voted for it intended it to mean.
There's plenty of scope for arguing that the situation has changed a great deal since then and that the constitution of the USA should be amended again as a result. But claiming that the existing amendment doesn't mean what it says and what the people who wrote it and who voted for it intended it to mean is a completely different thing and I think doing so is either ignorance or dishonesty. There's no doubt that the original intent of the amendment was to ensure that the people of the USA have a right to keep and bear arms that have the potential to be useful in a war or revolution.