I hate that phrase. It implies to many people that any level whatsoever of X is a danger to you.
Some examples: "There is no safe level of alcohol consumption" and "There is no safe level of lead".
These both may be technically true. That even one beer a year is worse for your body than complete abstinence. Or even a single fishing weight making incidental contact with your hand is worse then never having touched one.
But c'mon. The amount of risk posed by very low levels of consumption or exposure is so minuscule that we can safely (hah!) declare it okay.
I've seen people calling for lead to be banned from roofing flashing applications, and total bans on alcohol, citing these statements that "there is no safe level...".
You give me a reasonable definition of "safe", and I bet I can determine the safe levels of each of those things. The safe level of alcohol consumption is not 0.0000 units. It's somewhere above that. Same with lead exposure. You can have minimal exposure that results in no discernible difference in your quality of life. Where's that line?