Why do some people claim to be open-minded when they are not?

Ask somebody that if conclusive scientific evidence completely invalidated their beliefs or world-view, would they change them to reflect this new knowledge? If the answer is no, or that no such scientific discovery could ever happen, they are not open-minded.

Because you probably assume that if they were open minded they would agree with you. Thats not being open-minded. Thats being gullible, and believing anything somebody says. Being open minded is being able to accept new evidence, and making a decision based on that. Doesn't mean that. evidence will change ones mind. Only that one would consider it.

perhaps you're misunderstanding what "open minded" means

for instance, agreeing to acknowledge insane ideas of others isn't properly open minded

my mother is a great fan of saying everyone is entitled to their opinion

though .. its not hard to come up with opinions that are obviously invalid

gays should be killed? .. umm no

children should be allowed to enter sexual relationships if they want? .. noooo

women should keep their mouths shut? ... not on my watch

so

not opened minded to ludicrous ideas doesn't mean Im not open minded but simply capable of distinguishing genuinely legitimate ideas from nonsense

they do not understand what being open minded means

It's more PC that way. lol