Because diverse opinions lead to better end products. Having homogenized groups of people means you're leaving some viewpoints out, and those viewpoints have sometimes been extremely helpful for me as a software developer.
To moderators/downvoters: It is said that defending a cause with bad arguments is the most pernicious way to combat it. Similarly, resorting to authority and censorship to defend a cause must be the surest way to ruin it.
We have seen sexism actually grow in the last decades in this field, and i start to worry that this attitude of dealing with it with the argument of authority or other threats on one's carrier may just be one of the causes that we are slowly losing this ideological battle. Or maybe just a symptom?