Free Markets
For a long time now, I have been thinking about the concept of free markets, and its practicality. On the face of it, it is an amazingly elegant system, with inbuilt checks and balances. The "invisible hand" ensures that things are in line.

However, I strongly believe that it is highly impractical and un-implementable. It exists only in theory, and requires too many "perfect conditions" to work, which, of course, do not exist in reality. I remember a joke that demonstrates this:

Milton Friedman and his wife are shopping at the local market, when the lady exclaims:
"Look dear, there is a $100 bill lying on the road!"
To this, Friedman replies, without looking down:
"That's impossible dear. If it really was a $100 bill, someone would have picked it up by now."