It's an environmental concern. An oil spill causes harm to the ecosystem, and if the response to it isn't correct, the damage can spread or future parties won't be particularly careful.
Sorry, probably not the most fitting analogy. And I think I might have attached my reply to the wrong parent comment.
What I was trying to express was that if tmux had changed itself to accommodate systemd, this would have negatively affected the Linux "environment" by making it more acceptable for breaking changes in underpinnings to occur. By future parties not being particularly careful, I meant that this could easily lead to "screen, tmux, and pulseaudio agreed to run as a systemd delegate, and we already wrote the code expecting that you would, so we see this as your bug, not ours." This is particularly concerning as a behavior because RedHat has the money to buy its way.
