It's a bit of both, innit? There are MGIF cyclist the same as MGIF drivers. There are swathes of new converts to cycling who are seduced by the Strava Syndrome (whether or not they actually use Strava). I recognise Jane's narrative, I was there too. it takes a maturity of cycling perspective to step back from the "race" and enjoy the ride and hey, five years ago most of these riders weren't on bikes. Ain't that fucking fantastic?
We're living in changing times. Personally, I don't enjoy sharing the CS at busy times, but that's a choice. I can either ride roads at basically my own speed or I can share the safe CS with other cyclists by slowing down.
And no, I'm far from perfect. I will ride fast if it is safe and I get the chance, and I have to put serious effort into not intimidating slower riders; I hope I mostly do that now.