“Protect Your Personal Space with Mace”

「 催涙ガススプレーで個人のスペースを守って」アメリカでは、危険じゃないときにでも、催涙ガスを使ってもいいのでしょうか?

Riding the BART, the San Francisco Bay Area transit line, I was surprised to see this ad for mace, with the offer to get a 30% discount by typing in BART during the online check-out.

The idea that you can use a powerful chemical irritant to create a four meter wide personal space in public seems laughable in a dense city like Tokyo. Here, you can wear a face mask and maybe get a few extra centimeters of personal space as people may be afraid of influenza. To get 4 meters of space, you would have to smell very bad.

Are there other ways to feel safe in public? In the US, is it really OK to use mace when you are not being attacked and just want some extra breathing room?