I'd agree that it's a two-edged sword, but 1) Keeping standards high is not our only goal, and being welcoming is good for other purposes, and 2) I think there are better ways to be unwelcoming to low-quality people that cause less collateral unwelcomingness to good people.
Below is a message I just got from jackk. Some specifics have been redacted 1) so that we can discuss general policy rather than the details of this specific case 2) because presumption of innocence, just in case there happens to be an innocuous explanation to this.
So... thoughts? I have mod powers, but when I was granted them I was basically just told to use them to fight spam; there was never any discussion of any other policy, and I don't feel like I have the authority to decide on the suitable course of action without consulting the rest of the community.