To BlueState folk who say the 2nd Amendment is a remnant from Revolutionary days with no meaning today, when, may I ask, did it become such?

"To invade the mainland United States would prove most difficult because behind every blade of grass is an American with a rifle."  

They might answer the Second Amendment lost its meaning when the US adopted a military in lieu of a well regulated militia.

roughly around the Civil War is when the role of a standing army became both obvious and the national policy.  It is at about this time frame when the traditional role of the militia became obsolete, although we still have the "Militia" in terms of the National Guard.

It isn't exactly a case of the 2nd amendment being a remnant of its time so much as serving little purpose for its original intention, along with the advancements in technology which rendered guns into efficient killing machines that are used primarily for anything and everything EXCEPT what the 2nd amendment defined as the purpose for the "right".

I don't have a problem with guns of themselves, but any realistic observer can see that the murder and mayhem that guns permit to happen are not beneficial to a democratic society, so some controls on guns is the only sane solution.

No one says it has no meaning today. What we say is that the full amendment refers to a "well-regulated militia". Regulations are what we want, and the Constitution permits them. 

The Supreme Court [which is not synonymous with "blue state folk"] did not interpret the Second  Amendment as extending to individuals the right to bear arms unconnected with service in a militia until 2008, in a case filed by Heller. Look it up under "Heller, individual right to bear arms" if you don't believe me.

I'm glad you asked!  It became such when the Constitution was ratified.  1789.

The Constitution replaced state militias with a federal 'standing army'.  This was a controversial decision and there was a lot of argument about it.  In the end a compromise was reached.  We would still have a federal standing army but states would be allowed to keep their militias to put down small local insurgencies ( like Shay's Rebellion) and to deal with Indian attacks.  That's what the 2nd Amendment was originally about.

When did the 2nd Amendment become about everyone's right to own as many guns as he wanted, of whatever type?  And to carry them to school and church and Walmart and Starbucks?  Much later.

I need a list or you just made that statement up