If there's evil aliens out there, contact isn't the problem, it's discovery. No alien species is going to raid Earth for resources simply because they discover we can communicate with them. They would be more likely to raid Earth only because it happened to be on their schedule of planets to raid. And I would bet the planets would be sorted by distance and usefulness of resources, not by transmission of signals from life forms. And finally, any species capable of spanning solar systems and mining resources, could possibly be able to synthesize their own elements, eliminating any potential need to even seek out Earth-like planets.

-swb April 28th '10