One can empathically agree that such injustice, and any injustice, sucks, and still advocate compartmentalizing between institutions of the society writ large. That unprofitable path is not Basecamp's to bear. Not all injustices of the society receive a corresponding level of PR and therefore can be equally leveraged in the context of employee activism in a private enterprise.
If rank ordering of the issues of the society is left to the ripples made by affluential corporate citizens, that will introduce a host of biases that will alienate the full set of citizens of the democracy, and will likely create its own class of injustices.
The issue is not about surgically removing politics from work, it is to prevent its (mis)use as a backchannel.
To be clear, I feel equally strongly against corporate activism at the C-level or at the corporate identity level. But most employee activism is not only not a counter to that, it amplifies and parasitizes those very dynamics.