I'm not saying this isn't a problem, but I am extremely skeptical it is a problem caused by Big Bad Evil Apple doing Big Bad Evil things.
This could be (and I suspect very likely is) a problem with your iPad's SIM that you could check by powering off the iPad, removing the SIM and turning it back on again. It could be that there's some kind of corruption that you might need to fix by connecting it up to iTunes or even bringing to the dreaded Genius Bar. It could conceivably be some weird bug in iOS that has somehow sprung up and turned your iPad into a flat flowerpot. All of these things suck! But what it is not is Apple forcing you to "authorize" your iPad in order to let it boot up.
Do you disagree?
(I am nowhere near a "Genius Bar".)
https://support.apple.com/en-us/HT208987
Replacing the sim card in a device immediately triggers activation (e.g. to stop someone from using a stolen, passwordless device as their own). So, if the sim went bad, it seems plausible that the device might need to re-activate.
A bit of Googling shows the "Activation Lock" screen as a screen that says, well, "Activation Lock"; I think it's really a separate thing. If that's what happened to the OP, then it can be unlocked from the web:
Also, do you know if I could have prevented this by removing the SIM before it happened?
Do you have a mobile phone? Pop it out, put it in the iPad, activate it, take it out again.
In New Zealand, where I’m from, you can get SIM cards from supermarkets, petrol stations, convenience stores …