I certainly don't have a scientific background. I've picked up a lot over the last few years by getting into these topics.
The problem with using the colloquial definition of theory is it leads people to say things like "It's only a theory." Which is a complete misunderstanding of the significance of a scientific theory. I think its useful for lay people to know the scientific definition so that they understand what is meant when they hear scientists talking.
I try to use "hypothesis" instead of theory, which is what the colloquial definition is really getting at.