Fact: all swans are white.

Well, no, the swans in Australia are black (and just as beautiful).

The key is evidence. The evidence to date is .... But sometimes the evidence is also based on evidence to date. So instead of making flat assertions, we need to cite evidence and acknowledge uncertainties.

The problem is that some/many people insist on certainty, they have low tolerance for uncertainty.

Good, honest scientists have learned to live with uncertainty and make breakthrough-progress anyway (or in some cases because of uncertainty, think quantum computing).

The proof is in the pudding: What of any value whatsoever have evidence-free theories ever contributed to the public good?