Another application of the ad hominem fallacy questions...

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Another application of the ad hominem fallacy questions... Let's say there is an expert who holds a doctorate and masters in their field of specialty. They have worked in their field for 30+ years. They have received grants from government sources, but also the private sector (which as I understand, is not uncommon). They are peer reviewed and published. Now let's say that they present a study, with all its evidences and reasoning. But one of the associations this expert is affiliated with has a particular worldview. It is claimed, that because of that affiliation, there exists a conflict of interest and a strongly expressed bias (perhaps a mission statement or motto). As a result, this expert cannot be trusted, has a significant loss of credibility, and the reasoning and evidences provided in any study therefore, should be thrown out, it does not need to be addressed or evaluated. To me, it seems rather odd. The argument presented ought to be evaluated as if it is made anonymously. The argument, study, research ought to stand or fall on its own merits. But because the claim maker here (the field expert) is associated with a particular organization, all work done, conclusion, research, testimony, opinions are less credible and do not need to be addressed if there are competing conclusions, research, testimonies, opinions, etc... if they have no affiliations with biased organizations. So is the ad hominem fallacy being committed here? Or is it the case that not all arguments actually need to be evaluated and instead, there are times when we can instead, simply attack the argument maker?