You are quite wrong "laser777." I need no 'credibility' to make a valid argument. Is a young child credible when it comes to science? Has he any degree or prestige or accolades? And if he observes something and makes a verifiable claim that is wise and correct is the claim invalid or true? Of course, it's true! By your insistence on 'credibility' you may even suspend your own critical thinking. If one who you deem 'credible' comes along, you are already biased in how you will hear him. You may be less likely to consider critically what he tells you.
Stick to the argument itself. Let the bare naked fact either stand or fall on its own accord. Who cares in whose mouth it resides?
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