We now have a policy of pre-emptive strikes against potential threats. Don't you think this might lead to equivalent policies by other nations? Perhaps even against us?
Yes, it might. This is obviously a potentially dangerous 2-edged sword that must be used wisely.
The wisdom of a course of action or inaction is often determined with 20/20 hindsight. A pre-emptive strike against Germany in 1935 when Hitler renounced the Versaille Treaty and declared Nazi Germany's intention to re-arm would have saved 40 million lives in the 1940's. On the flip side, the use of the claim "pre-emptive strike in self defense" can be abused to justify just about any military adventure.
Each case much be honestly debated on it's own merits as blanket rules seldom apply in the Real World.