Of all the graduate students I met, you could more or less divide them into two classes. The first class wanted the PhD as a means to an end, such as doing research, or getting a professorship. The second class had more abstract and less well-defined goals. Sometimes that meant generally "doing good for the world", or "seemed like the right thing to do", or "the working world sucks, this is the lesser of two evils".
I fell into the second class.
I spent three years doing computer science grad school at UNC. I passed my dissertation proposal and then decided to leave.
I don't resent those three years and did learn a few things along the way.
Getting a PhD is ultimately about getting 5 other PhD's to sign off on your dissertation. At least that's the requirement in computer science at UNC. I wish that had been more clear to me at the beginning.
Graduate school as a means of stalling to find something you love to work on is not a horrible way to go. In the meantime you might solve a few problems. I also consider it noble that we (graduate students) as a whole are willing to do the nation's research for such little pay.
Had I thought long and hard about why I was doing the PhD to being with, I may not have started. But life always charges its own tuition.
From the article "As long as you have an answer that you believe in passionately, then that's enough." My three years in graduate school taught me that the most. Find something you love, or least have passion and do that. It may be a silly belief, but it's worth believing in.