My requirements for someone's ethical opinions to be "valid" are that they don't criticize the field of ethics as useless. I guess that is a "requirement" I have, but it's a pretty nitpicking, useless distinction to make.

If someone criticizes the French language, but doesn't speak a word of French, sorry, but I don't have much respect for their opinion on French.

And no, I don't "assume they aren't well thought out," because many of these people have explicitly said philosophy is a waste of time.