While it’s easy to say “because theists realize that their religion does not stand up to logical examination”, the reality is far more nuanced. First, lets clarify a few things..
- Theists tend to hate/dislike atheists because many holy books have precise scripture against blasphemy and-or nonbelievers and how to handle them, and atheists tend to fall into both camps.
- Theists that listen to atheist arguments generally are not examining themselves logically. Something that is core to them is getting challenged, and it feels like an honest to goodness attack.
This is because many theists have subconsciously gathered a bunch of incidental anecdotal data that confirms their beliefs, and have some of the strongest confirmation bias of all time. That time when they prayed before a big test and got a high score? That time when they prayed their mother would get better and she did? The multiple stories they heard from friends talking about similar experiences?
Everything adds up and compounds in their minds as evidence, and when one challenges that, you’re actually challenging the scores upon scores of anecdotal evidence they’ve accrued over time. Logically, they’re being consistent, and you’re offending every single link they have of those memories. So of course they’d lash out against it.
Their brains close up to new input, and if anything, its been shown that this confirmation bias strengthens when challenged. This is known as the backfire or blowback effect. Confirmation bias is one of the biggest survival instinct of the human mind, because it’s strongly linked to the mind and how it deals with conditioned responses (“Pavlov’s dog”), and everyone has to deal with it. It goes to teaching a person on things to seek and things to avoid, and religion fills that expertly.
The best way to argue against theists is not to argue against their beliefs, but to get them to understand why gathering metadata about something is far more important than anecdotal evidence, and why most modern systems of society discount anecdotal evidence as essentially worthless.. from science to justice to business, anecdotes are typically seen as a guide at best and junk more commonly. One could realistically find the answer to any question they want using anecdotes.
And then, only after lining all your ducks in a row, should you then talk about how anecdotes also apply to beliefs. And do so respectfully and tactfully. Attacking them and telling them they are idiots is easily the worst way to get them to change their minds, or any onlookers.