But in a public forum such as this, calling a community toxic can, and will, keep people from looking in to to the associated project any further. If you have specifics, you should say them - public spaces are the right place to out toxic communities. But, people on the internet throwing around words like "toxic" without substantiation can be really damaging to communities by preventing growth.

Please substantiate - I'm not involved in the Nix community much but whenever I've been in the #nixos IRC channel, they've been super helpful.