My experience of writing that switches pronouns arbitrarily is that it continually draws attention to the ratio of men and women in programming, which makes the lack of women more obvious. I first noticed this in an advanced physics course where in deference to the presence of a lone woman in the course the professor consistently said "he or she". Except that it was a conscious attempt and served to draw attention every time to the lone she who clearly looked uncomfortable.

This is why I prefer to use singular they instead. It is less annoying, less likely to make people uncomfortable, and can easily be seen to include people no matter what their gender happens to be. It even includes those whose gender is ambiguous in some way.

It is a small thing, but my world view is that small improvements like this add up to create a more generally welcoming atmosphere.