A belief that the universe is black and white and that their answers are fact will cause them to be shitty scientists, not to mention the greater propensity to be shitty people... which will further cause them to be shitty professionals. That's the point.
That's an example of the kind of outlook I was thinking about when I wrote that prejudice directed against such people would impair their progress and their ability to contribute more than their actual belief in creationism would.
I think that one can readily confirm that it's possible to be a good scientist and also be a creationist and/or "intelligent design" adherent by just looking at examples of people who made great scientific contributions before the current secular outlook was as widespread as it is now. I've seen things where people will say, for instance, that Issac Newton believed in alchemy in order to diminish him because he was a deeply religious man. But the guy was still a great scientist. One of the greatest in history. And I think we both know I can find plenty of others from previous times.
I could probably find examples of people from the current times as well who are creationists and who also do well in their chosen field. I know at least two engineers, for instance, who are like that. Of course you have to take my word for it. One of them tendered his resignation so he could go to a seminary and become a minister. His employer, a large petrochemical company, did not want to lose him so said it would accommodate him however he wished in order to keep him working for them while he also went to seminary. He got extremely flexible terms, working when he could and wanted to as an engineer. Also allowed to work from wherever he was instead of having to go to a duty station. He didn't go in with the intent of getting special terms from them either. He went in to say, "I'm resigning to become a minister."
Now, when an employer does something like that it tells me it views what somebody has to offer as valuable. I guess you can say that his beliefs impaired his ability to contribute because he was going to quit being an engineer in order to become a minister. But you certainly can't say his beliefs impaired his ability to be a good engineer.