You have consistently failed to demonstrate that this is an issue. You seem to be conflating it being hard for *you* to read with it being generally bad and hard to read.
Despite your best efforts, 1+1 ≠ 3. Keeping the font the same size does not effectively mean it is smaller, it means it's the same damn size.
You are clearly using a screen for which the forum default font was hard to read for you. That sucks, maybe you should use stylus or another extension to make it larger, or enable text-only zooming and zoom in, rather than forcing your change on everyone while relying on appeals to authority vis-a-viz "standard web design"
Do you ever read news.ycombinator.com? The font there is even smaller, it is a site run and used by software and web developer professionals, and it is well indexed in google. Your arguments are but a figleaf to cover up the fact that you want your personal preference enforced on everyone else. And you don't even even have popular opinion here to support you, you have nothing but your opinion and appeals to "good web design norm".
As others said, most websites suck ass these days. We don't want the norm. We want what works for the majority of us, what we had. Not "a good portion of readers", which with your axe-grinding-philosophy could be interpreted as an even smaller subset than 40% by the way. Funny that.