I'll venture a guess you've never heard of the git hosts that only offer private plans. Allowing people to post public code for free is fundamental to our business model and a major reason why we're successful.
I haven't, though I haven't had the need for one either. But if they exist and they're decent, you don't think I would find them if I researched for a git host?
I don't argue with you that freemium works in the short and probably medium term, and it's great advertising. You have a great service going, and I think in your case, you build a lot of good will among developers hosting public code for free. But in the long run, in the general case, and assuming no network effects, I think there's a way to undercut such business models by focusing 100% on the paying customers.