It's next to pointless for anyone to learn martial arts for self-defence unless they're at some enhanced risk of violence. In most western countries, the likelihood of being involved in a fight as an adult is pretty low. There is also the phenomenon of feeling safer and that you can handle yourself, which discourages people from leaving or de-escalating a situation when they should. On the other hand, the sheer amount of time and money it costs, and the limited effectiveness it actually gives a person in a real-world chaotic altercation, make me think that for self-defence it's quite a poor investment.
That being said, I've practised martial arts for 10 years and have moved to Japan to continue my practice. There are great reasons to do martial arts but I'm always critical of self-defence as a primary motivation.