If you actively try to avoid software that is licensed under BSD or ISC, only Gnu’s Marxist license, then that means you won’t use OpenSSH or the security tools ported over from OpenBSD into both Linux and Android and will not use an operating system or programs that have been compiled with LLVM/Clang.
OP did say "wherever possible", not "without any compromises"; I agree that it would be very challenging to try and live on purely GPL software, but it just seems like they're looking for potential alternatives. I think it's admirable given their stance on libre software.
Gnu's Marxist license
This seems like such a blanket statement designed to put down copyleft advocates "because communism". Do you think the right to repair movement - which advocates for control over one's hardware (in contrast to software) - is also Marxist? I consider these two movements as practically adjacent to one another.
I prioritize system security, and for that I only care about open source and reject free/libre software due to all of its built-in political implications. But also defend the right for people to make proprietary software. I won’t use it, but defend people’s right to make it.
I ask the following more out of curiousity than argumentatively, because I still don't quite understand this position: do you still encourage people to use libre software in this case? If libre software is better than proprietary software, why shouldn't we strive for a world where all software is libre? Is there any reason for software to not respect its users' freedoms? I'm not saying that we should all be hardcore GPL-only-or-die enthusiasts, either; rather that it seems reasonable to aim for a life free of proprietary software, one step at a time. In my opinion, copyleft can accomplish that better than permissive licenses would.
I'm confused with some of the comments here - isn't OP asking why the BSD 3-Clause doesn't include a clause preventing patent treachery, which would be a good clause to have?
In any case, this is why the FSF recommends the Apache 2.0 license over other permissive licenses: https://www.gnu.org/licenses/license-list.html#apache2