While I understand your vantage, I firmly believe that it should be opt-in, rather than opt-out, even if only for ethical reasons.
Furthermore, having any kind of telemetry enabled by default and opt-out is — as you noted — a very contentious affair in this day and age, and especially so in light of big tech companies like Google, Canonical, Meta/Facebook and even Mozilla resorting to telemetry that is either opt-out or doesn’t even allow for opting out.
We’ve already had quite a few issues here at the forum over the past five years with members who wrongfully suspected that we already had telemetry enabled because of the ping, and from this experience, I firmly believe that having it enabled by default — even if only on new installs, not to mention pushing it out onto existing installations as well via an update — will come around to bite us in the hind side quite quickly and quite ferociously.
If anything, then past experiences have demonstrated that it doesn’t take a whole lot — as the matter of fact, a storm in a teacup is already enough — for Manjaro users to jump ship in droves and leave Manjaro for Arch proper, Endeavour OS, Garuda, or similar distributions.
I think this issue is worth serious contemplation, and especially so because @philm gave the members his word that any upcoming telemetry features in Manjaro would be opt-in only — which is also how KDE do it, by the way.
Additional note: Manjaro Metrics looks cool, but the “tooltips” when hovering over certain elements often fall outside of the browser window’s dimensions. Perhaps something to tweak a little? 