Perhaps, like me, you've been agonizing over that question for a long time. Perhaps you think a PhD will help you gain an advantage in this crazy economy. Maybe you'd like a ticket to the academic lottery. Or maybe you want to avoid the real world for awhile.
These are just a few reasons why people pursue PhDs, but what reason is good enough to justify another 3-10 years of schooling?
If you think I'm going to claim that fiery, passionate love for research is the only legitimate reason to go for a PhD, I actually think that is one of the worst reasons. Sure, passion is great, but major life decisions shouldn't solely be based upon feelings. The long, grueling, and often unfruitful work of a PhD program can make those feelings fade.
Deciding whether or not to do a PhD is a very personal decision, and my only advice is that before embarking on such a big commitment, be sure to have a clear plan and do a thorough cost-benefit analysis.