I am not sure that I understand your point: as you probably know, Bernie Sanders is not a communist, so why would anyone associate his persona with the horrors of authoritarian communist regimes?
The difference between "communist", "socialist" and "democratic socialist" is mostly marketing branding. Same ideology, different wrapping. But my point is not about Sanders but about the fact that people disagree on a lot of things, and if open source organizations start excluding people because somebody could disagree with them on political questions we'll get into a bad place quite fast.
Of course, singling out communism is not fair - I could name many other ideologies that some people may be very uncomfortable with, especially if you pick out the worst statements you could find, interpret it in worst and most uncharitable light possible and pretend that anybody who have ever agreed with anything in that ideology also fully agrees with that maximally uncharitable interpretation. It would be rather sad safe place if that policy would be carried to its logical conclusion.
But of course it would never happen. I can't imagine anybody being kicked out of a conference for ever wearing (even outside of the conference context) Che Guevara t-shirt or being photographed in presence of hammer-and-sickle flag (and I'm not even talking about religious symbols, most Abrahamic religions at least having very dark pasts and rather ambiguous present). It would be carried out arbitrarily and capriciously, following where current political winds are blowing and what tribal pressure groups happen to be more vocal and scare the organizers the most. That makes it not only a bad policy, but also a hypocritical one.