Fair enough, but could is enough to play on people's fears. Immigrant X could be a terrorist. Food additive Y could cause cancer. You can't then claim you didn't say "would".

Note that things like tobacco cancer warnings use use can/could not will/would, and the intent of the message is still clear.

"SURGEON GENERAL WARNING: Cigar Smoking Can Cause Lung Cancer And Heart Disease."

"WARNING: This product can cause mouth cancer."