The term professional is clearly applicable to software engineers working on open source projects, just as it is for lawyers doing pro bono work, and just like

The term professional is clearly applicable to software engineers working on open source projects, just as it is for lawyers doing pro bono work, and just like a plumber fixing his neighbors' sink for free is still performing his trade and expected to do work that upholds its standards. No one is required to do any work for an open source project, but they are expected to behave in a professional manner and plenty of people have been rightly criticized here when they acted inappropriately as part of an open source team. Its debatable whether OP is right, but there's at least a case to be made that taking down documentation that was not costing any money to host for the sole purpose of making an unrelated statement (not one targeted at their customers, just society in general) does damage the professional reputation of the team and its product.