We've discussed this many times. Add I know I can't change your mind.
But for those who haven't heard my reasons here they are.
- The JSA heroes aren't tied to WWII or the 40's, the way Captain America and other heroes created to fight the Axis powers are. The only JSAer who's origin was tied to the war is Wonder Woman. And that connection was left in the dust decades ago. Even Wonder Woman's membership is up for question at this point. The various heroes who make up the JSA were created as crime fighters, not war fighters.
- Wonder Woman, Batman and Superman were allowed to cut ties with the 40's and WWII, so why not the rest of the JSA?
- The JSA strip ran for 10 years, from 1940 to 1950. So half of its run was published after the war ended. And arguably, some of its best stories took place after the war ended. Of the stories that did take place in the war years. half again were not war related. They spent more time fighting crooks and mad scientists than the Axis.
- What I think of as the iconic line up is from the post war years: Flash, Green Lantern, Hawkman, the Atom, Wonder Woman, Johnny Thunder, Dr. Mid-Nite and Black Canary. In fact Flash and GL sat out most of the war time issues because they were only Honorary Members in those years.
- What is the advantage of keeping them tied to WWII, outside of nostalgia? The characters would have to be pushing 100 years of age if they are living in 2016. Do we need an entire team of nonagenarians? The older they get the older or more unlikely their kids (Infinity Inc) are.
- No mention of WWII was made when the JSA was brought back in the early 60s. The first mention comes over a decade later when the origin of the JSA is told for the first time on 1977's DC Special #29. I doesn't go full swing until the 80's and the All-Star Squadron.
- The 70's All-Star revival is great. The blueprint for what the JSA would become in the 2000's: Older heroes and legacies. You don't need the WWII connection for that, just a previous generation of heroes..
When Barry Allen meets Jay for the first time, they outright state that Jay was active since the 40s, aka he's a WW2 hero. WW2 is as essential to the JSA as it is to Captain America. Without WW2, All-Star Squadron, Young All-Stars, Justice Society (90s mini-series), JSA Returns, JSA, and Justice Society of America wouldn't exist. All those series have deep ties to the teams WW2 history (especially AS Squadron, obviously).
Superman, Batman and Wonder Woman got disconnected from WW2 because of the Earth 1/Earth 2 stuff, which is fine. The other JSAers were WW2 heroes even when they were brought back, being active in the 40s. The prime versions of the Trinity were all basically rebooted, but the core JSA weren't. Even if they weren't created specifically for WW2, they have been WW2 heroes from 1942 until 2011.
Let's do some math. Let's be very generous and pretend the JSA weren't mentioned as WW2 heroes from their return until 1977 (they were, like I said above, but let's ignore that). So, from 1942 until All Star Comics demise in 1951 they were WW2 or WW2 connected heroes. Then, from 1977 until 2011 a lot (probably a majority after the All Star Comics run ended and All Star Squadron began) had at least some connection to the WW2 roots. So, that's 43 years with a direct WW 2 connection. The jSA was basically in limbo from 1951 until Flash of two worlds, so we won't count those years in anything.
So, using the (false) premise that they weren't WW2 heroes when they came back from limbo, they weren't WW2 heroes from 1961-1977, then from August 2011 to present. Let's also add 1939-1941, the pre-war years. So, about 23 years as not a WW2 team, and that's being very generous and ignoring references to them fighting in the 40s/WW2 during the 61-77 era. So, 43 years as a WW2 team (even if we cut off the directly post war years, its still 36-37 years as a WW2 team) compared to 23 years. You could even argue only 5 years if you don't ignore the fact that the 1961-1977 era were also WW2 heroes and just didn't mention it as much. you could even say it could be 0 years if you take what I said before and also don't count the New 52 stuff, since they never call themselves the JSA in the New 52 and the majority of the rebooted characters have no relation to the pre-New 52 characters except for the name, and a few New 52 versions (like Dr. Fate and Hourman) don't even share a name or any backstory with the pre-New 52 versions.
Even if you want to try to justify the JSA having any time post-1942 as not having a WW 2 connection, the JSA still spent spent 36-43 years with direct WW2 connections, and (in my opinion) all the great JSA series and stories are definitely connected to WW2. So, I'd say its essential for the team to be connected to WW2, at least that's where my opinion comes from.