Some criticisms include accusations of white guilt. This assumes that everyone wearing a safety pin is A) white and B) not a member of any oppressed group. Since women are wearing them, and women are a disadvantaged group -- especially with the pussy grabber in chief -- that disproves the argument. Not to mention all the queers, people with invisible disabilities, foreign-born citizens, and everyone else the bigots would like to abuse. Offering yourself as safe space isn't slacktivism. It's advertising yourself as an upstander. Because we need to remember this shit and that challenging bigots is risky.
I try to maintain my little corner of the web as safe space. It's not perfect, because I've got a temper and some days I am out of spoons to fake being civil. But I try. I generally discourage people from picking on each other. I welcome a wide range of people and traits. By and large, I don't make a fuss over many things that other folks are fussy about. So be yourself, and don't be a dick. SOMEbody has to be the grownup.