The case for Linuxism is that Linux has the underlying tools applications require to deliver the user experience users want, and if OpenBSD (and this is from an OpenBSD list) wants to run those applications it should provide the same tools.
A better case against Linuxism is that portability encourages modularity, which is good for reasons far beyond portability. Having to do some things in a different module because they can't be done the same way on all systems encourages you to separate concerns, which leads to code that's easier to reason about and, therefore, less likely to be buggy.
The historical perspective is "You think this is bad, sonny, be glad you're not trying to convince people to play nice with Eunice." (Eunice was a Unix-like environment running on VAX/VMS.)
A better case against Linuxism is that portability encourages modularity, which is good for reasons far beyond portability. Having to do some things in a different module because they can't be done the same way on all systems encourages you to separate concerns, which leads to code that's easier to reason about and, therefore, less likely to be buggy.
The historical perspective is "You think this is bad, sonny, be glad you're not trying to convince people to play nice with Eunice." (Eunice was a Unix-like environment running on VAX/VMS.)