Scott Wiener is pointing out that abstinence isn't a public health strategy. People have sex. Abstinence doesn't work for sex ed. It doesn't work for the HIV/ AIDS crisis either. Abstinence obscures the activity and heightens the risks.
What works is educating people around the risks and what to look for. Reduce the harm of their behavior. Ask them to stay home if they are feeling sick or have unusual lesions (monkeypox doesn't appear to spread from asymptomatic carriers). Help them get tested and vaccinated.
Also for that matter we shouldn't collectivize gay men here. Gay men aren't all promiscuous and monkeypox isn't inherently a gay sex disease. That certainly doesn't help avoid stigma. There's a tactful way to frame the risk of exposure as highest among MSM with multiple sex partners at present. But as this outbreak continues we may see the exposure risk change to other social networks in much the same way HIV exposure risk was higher in gay communities, but shifted to intravenous drug users and heterosexual subgroups.