Competition between Traders

Any financial market has competition, the competition of the trading strategies and Expert Advisors (EAs).
Is there any competition between traders?
What is the reason to share the very competitive and valuable information on the financial forums and blogs?
Don’t you think that if many traders will use the same profitable strategy that it’s became useless.

Here is Darkstar's widely read post about the pros and cons of sharing one's strategy. The whole thread is worth reading, IMO.