The diversity I'm talking about is in personality types. There's a lot of people, even on Hacker News, even in this thread, that would be excellent technical contributors to the Linux Kernel, except they have a personality type that requires them to spend more emotional energy dealing with verbal abuse, either directed at them, or just being flung about.
As you say, size isn't the most important measure of a contributor pool.
In my mind, angry, hateful language, especially if it is accepted by the whole, will greatly limit the amount of talent available.
Good development and merge practices has and will continue to keep bad code out.
And note, I have not said anything about being warm, friendly or inviting. I'm not necessarily suggesting those be specific goals.
Finally, nowhere have I suggested that anybody stop working on features, and instead 'encourage the surrounding community to be nicer to one another'.
There is a very real possibility that angry language results in an increased ability to ship code by discouraging more net-negative contributions than net-positive ones.
I'm not willing to assume that a more diverse project and larger potential contributor pool will automatically produce better code. Not all contributors are of equal value. Some contributors are of net-negative value, particularly those like Kay who persist in such. It is highly desirable to limit the potential contributor pool to as few of those individuals as possible.
Size is not the sole meaningful measure of a contributor pool. Quality is equally - and often more - important.
When dealing with matters tangential to a core purpose, sometimes the ends do justify the means. When was the last time you thanked an open source developer for stopping development on features you needed (perhaps permanently so) in order to encourage the surrounding community to be nicer to one another?