In my neighborhood, there are lots of homeless men, some of whom are drunk, high on meth, or off their meds. They engage regularly in the verbal harassment of women on the street, often making remarks far more aggressive than anything featured in Hollaback's video of catcalling in New York. I know this because women in my life—my wife, friends, workers at neighborhood stores and restaurants—share their experiences. Though I seldom witness catcalling or verbal harassment, I've come to understand how constant and burdensome it can be for women, especially when the words used are crude, violent, or degrading.
Activists who spread awareness of this problem are doing a public service. As the cumulative effect of individual comments becomes more widely understood, some men will stop catcalling, newly aware that the behavior isn't as innocuous as they imagined. Other men will tell catcalling colleagues at the proverbial construction site, "Dude, that's not cool." Slowly but surely, social norms will change.
Nor are viral videos the only way to attack the problem. In Venice, where I live, I strongly suspect that increasing the number of beds in Los Angeles homeless shelters and assigning social workers to neighborhood encampments would almost immediately lead to less harassment of female residents. Other neighborhoods are different. In Seville, Spain, where I often witnessed catcalling, blonde study-abroad students were besieged by definitely-not-homeless men.