Should I go for a PhD?

I know a person who studied nutrition science. As he/she didn’t find a job afterwards due to the “uselessness”(?) of that area, he/she appended some time for a dissertation. Having earned the PhD, he/she is now even more qualified as a jobless person (or rather, as a waiter/waitress). I tended to judge this case in a disparaging manner. I mean, c’mon, studying something useless, thus not finding a job, becoming even more professional in that useless area and thus being even less able to find a job. What’s the use?

Now, as I’m finishing my own studies, I really want to justify the use of mathematics by finding a good job. Through all the years non-scientists (e.g. medics(!)) were asking me what one can do with a degree in mathematics. I want to show off that I can choose between several offers all across Europe. This is indeed already starting today with probable possibilities in both Vienna and Munich. But both of them are postgraduate positions. What should I think of that? Am I in danger that someone walks up to me, saying, “Ha ha, so you really can’t make use of mathematics and therefore do a PhD!”?

Up to now I preferred to leer at the industry, as positions are lucrative, mathematics is applied, and mere mortals get in touch with the emerging products (like automobiles, digital entertainment, communication, medical diagnostics). But at least those two mentioned postgraduate positions go into the applied direction as well. So, I’m in no case up to doing some “weird”, abstract, theoretical stuff that no-one makes use of, even if I decide to go for a PhD.