Your distinction between 'doing science' and 'understanding science' is a valid one. Similar to the difference between simply being a soldier and actually fighting a war (not that science is a war, but it can get pretty competitive).
You don't need experience doing actual research to understand science and its implications. All you need is some basic education. I think a lot of non-scientists here do a pretty good job defending the principles of evolution without being professional biologists.
Problems only arise when people forget to recognize the boundaries of their education and the limits of their understanding.
This goes for non-scientists dicussing science and for scientists discussing topics outside their area of expertise.
I think we should encourage everyone to discuss their ideas about science, right or wrong, and those who do science professionally can help clarify things that relate to their areas of expertise. That's one of the most positive aspects of this board. The question of who is credible and who isn't is ultimately up to readers to decide for themselves.
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