Doing a PhD: Self-indulgent, or what?

That’s a question that’s been lingering in the back of my mind for a while.  I recognise that a lot of PhDs will make a difference, maybe even change the world, but I have serious doubts that my thesis will ever have such a positive effect.  So am I just being a little bit selfish and indulgent?  Could my time (and money) be spent more proactively in another way?  My old job – in Student Support – wasn’t exactly my chosen career, but it wasn’t horrible.  And I enjoyed making a difference to peoples’ lives, if only in a small way.  I think I might actually be missing that – having a social purpose, contributing to something larger than myself.  This PhD thing can be a jolly insular experience.  Perhaps I’m just thinking too much.  Hey, that’s my job, in a way.  Thinking and analysing and obsessing about stuff!