What is probably being misunderstood by a person who says, "but that's only a scientific theory"?

The person saying the word "only" before the scientific theory is not able to distinguish the general theory or a proposed idea and the proved scientific theory.

The proposed idea is the tentative statement and well-educated guess which has to be tested through the experiments whereas the scientific hypothesis is the proved and well-established statement. Also, the theory is the elaborate form of the hypothesis which explains the event in depth.

So saying only before the scientific theory proves that the person knows little about the theory and hypothesis.

answer; if congress didn't act on certain requests;