Stack Overflow removed the reputation penalty when down voting a question:
"Down votes no longer cost you, the down-voter, any reputation points on questions only."
- Stack Exchange podcast 06
I feel this will encourage users to down vote indiscriminately.
Questions are also an important part of Stack Overflow, this knowledge should also be protected.
In addition, this gives unrestricted power to all users to down vote questions. Who can promise no one will abuse the privilege?