Earlier quoted context omitted.
If I have a process that works for 95% of the people, why should I care about outliers who use Linux behind a VPN on a heavily customized version of Firefox?
Because they are standards compliant and you aren't, and you are legally required to provide an unsubscribe service or whatever without undue barriers around it.
Everything else - no.
But if I am using standards and they have an ad blocker that blocks some of the functioning of my site, am I also required to test my site against that?