I literally sit in cybersecurty chat channels where people who know tons still cannot get the "plenty of tools" to block this to work correctly. The ones that do have spent thousands on equipment and monitoring capabilities. You don't even come in with examples of how to do it properly, let alone for non-swe/network engineer/ families to do it. Just hand-waving away "i'm sure mobile devices could".
It's nothing like a parent bringing home the beers. In order to participate in education and social life your kids need access to the internet and devices. You parents are giving you a tool to do a job that comes with a negative externality of being able to access adult websites (and anything else on the internet).
It's not ridiculous for parents to vote for representatives who will put legal blocks in place to force a change since there's no way to vote with your dollar here, even if the source is religion where making children is a core tenant.
I'm very familiar with living with LDS. I'm in Idaho.