Efficiency is one of our values and vetting customers is time consuming and potentially distracting
Presumably policing employees for violating your code of conduct is also time consuming and potentially distracting. So how can it be worth having one if "efficiency" is your core value? That seems to be the contradiction at work here - they have the time to worry about the behaviour of their employees, but not their customers, so the answer must simply be that the only value they're really interested in is the value of money, no matter how dubious the source.
My opinion is that most people have some sort of limit of what they find ethically acceptable - I have quit one job during my career because I wasn't comfortable with the origin of the money I was earning, but I accept that other people's limits will be different to mine. And for sure I must have purchased stuff that is not massively ethical either, so there's no attempt at being pious and hypocritical here. It might be fun to test their patience : what if hundreds of software projects focused on criticising GitLab and targeting their management were uploaded? How long would their libertarian principles hold firm then? I think the excuse that "it's our company and we get to decide what we do and don't allow" would be rolled out pretty quickly then, thus invalidating their current argument.