The thing killing open-source is the people
shruubi.com
shruubi.com
Note: For this post I'm not trying to say anything one way or another about the complaints towards the social environment of the Kernel community, I find this a particularly poor point to use when arguing that message.
There are a tonne of smaller projects who will gratefully accept submissions and not be such a pain. It's easy to view Linux as the centre of the open source community, but in practice it's not.
A much easier way to get involved in open source is just to do so as part of your normal life - when you're using a library and find a bug, submit a fix - if there's a feature you've added and found useful, submit it as a PR. It might not be well received in every case, but it will in many.
I get that people use it to label things they don't like, it just seems like it is used as a catch all.
For instance, is bluntness that occasionally comes across as rudeness toxic? Is the use of expletives toxic? Etc.
I think something like excessive, pointless rudeness probably fits under toxic as a category, but it also more useful to just say that such and such is rude.
I've contributed to large-ish projects like Symfony2 with high standards, but the community was still encouraging.
Point being, I think the overall community and age of the project are the best indicators for determining how hostile contributing would be.
This is why leadership is so important, because without a leader, the human mob maintains a state of semi-cannibalism, feeding on itself. With a leader, they either stop doing that and get on with the project, or .. they eat their leader, and for a little period of time while doing that, forget about their own self-cannibalism long enough to actually get big things done.
In many open source projects, things go awry because the leader is trying to engage in aggressive cannibalization of 'others', and so the goals and purposes of the group are not propelled forward.
That being said, managing your new project like it was the LKML will probably be a kiss of death.
(edit: but to be clear, yes, toxic communities do exist and are a terrible blight on the wider universe of open source)
The incredibly competent men who run the show in authoritarian ways that appeal only to men just like themselves will slowly give way to communities built on negotiation, respect, and compromise -- humans will be humans.
Those who mutter the word feminism only in derisive tones will complain loudly as their world mutates, even as their own standards of normality and fairness change.
This world of computers has been the domain of such men for a long time, for a lot of reasons, but the days of this sort of thing are numbered. Computers are too important.