I want to specify my question to theism (it should apply to all ideas) as an example. Some people believe in theism. The sole reason why they believe is because someone else believes it too and everyone goes along with it. If someone tells me that I can't be 100% certain that there is no god I'm very perplexed. Of course I can't be 100% certain but there is a lot I can't be certain about for example conspiracy theories or unicorns.
We all accept that unicorns are imaginary and that conspiracy theories are made up. And if you try to use these / bring them up in a conversation it is not taken seriously, with good reason. Thanks to critical thinking we know that this is so unlikely to be true that we don't think about it. But the same thing can't be said about theism.
If enough people believed in a conspiracy theory and then started to say "how can you be 100% sure it didn't happen this way" this would lead to a big problem.
A solution would be to only consider/value ideas that can be proven or are likely.
Do we have to value/consider ideas just because they can't be disproven?
Is there any literature on this subject? What do you think about this?