Ok, a few answers to this:
(1) America was settled, at least initially, by religious fundamentalists who wanted to set up a sort of theocratic republic (before anyone jumps down my throat and says, “The founding fathers were not Christians” – yes, I know, I’m not talking about Jefferson or Paine or Franklin, the people who signed the Declaration of Independence and wrote the US Constitution – I’m talking about the people who went to America in the 1600s. This left a DEEP cultural idea in the American people that they were a ‘chosen people’ living in a ‘promised land’ etc. God loves America; so for an American not to love God back is seen as a sort of treason.
(2) The popular religion that developed in the USA, especially along the frontier and in the South, was anti-intellectual. Unlike in Italy, where the Catholics have a hierarchy and a trained priesthood, the dominant form of Christianity in the USA comes out of evangelical traditions and ‘revivalism’, where anyone with a spattering of Bible knowledge and a good shouting voice could start a church. This led to a very simplistic, literalist, bible-based theology. The broader education and humanist philosophy of the priests in catholic (and anglican and lutheran) churches in Europe mitigated against this trend and produced a religion which is in some ways more ‘porous’.
(3) More generally, the USA has an anti-intellectual culture. In most of continental Europe people look up to and respect ‘book learning’ and being a civilised, cultured human being. In the USA (in most parts) this would be looked down on – it’s what you DO that matters, how much money you make. This anti-intellectualism means that those who have a rational, scientific view of existence can easily be criticised as being ‘out of touch’ with ‘good honest god-fearing Americans’. (Read in redneck voice): ‘Them danged atheists thinks they is better than us folks, just cos they done got themselves a college edjikatishion’. It’s like the horrible reverse parody of the democratic ethos.
(4) Being part of a protestant church is a major commitment. It’s not something you just do as a social ritual, like catholicism can be. You have to make a choice, profess Jesus, get baptised by immersion, sign the members’ roll, turn up to meetings, sit on committees. This tends to harden the edges of the ‘in-group’ and the ‘out-group’. In a catholic country, everyone (or nearly so) is culturally catholic, even if they do not believe in god or go to church; you can’t be a ‘cultural baptist’ – you are either In or Out (and, according to the Ins, everything Out is evil).
(5) After the second world war, the USA had a massive internal propaganda system designed to attack socialism and the left. Communists were ‘atheists’, Communists were bad and anti-American, ergo atheists were bad and anti-American.
(6) The USA does not have a good welfare system. Indeed, the whole country is based on a sort of individualist myth, where the only reason that one guy is working 70 hours a week and struggling to get by with two minimum wage jobs and no healthcare, while someone sits by their pool and has a private jet, is that the first one is ‘lazy’ (i.e. unfavoured by God – remember, Protestant God Wants You to Work Hard) and the second is ‘hardworking’ (i.e. Blessed by God). This means that: (i) there is a lot of fear – fear of sickness, fear of unemployment, fear of annoying the boss, fear of random economic actions outside your control. Fear drives people into fearful, nasty, exclusive versions of religion – a ‘hunker down’ against ‘the world’; (ii) people need the social network and support provided by a church, because the state provides so little – thus atheists are a threat to people because people are terrified of being convinced by them, having to leave the church, and thus losing their social network and support system.
(7) This is the crucial one – it draws on 1 and 5, but goes beyond them and is vitally relevant today: There is, in the USA, a thing called ‘Christianity’ that has little to do with Christianity as it is generally understood in Europe, or in the longer view of the Christian tradition. It is a heavily nationalistic, militaristic, masculine, authoritarian cult, with Jesus as the Cadillac-Driving All-American Hero who has come to save his Chosen People from Gayness, Socialised Medicine, Arabs and Long Haired Hippies. This might best be called, “Amerireligion”. This was deliberately created after the 1960s by the American right, who wanted a way to stop the changes begun by the Progressive Era and the New Deal and to restore the dominance of the old ruling class. The civil rights and anti-vietnam war era brought it to a head. The right saw an opportunity to appeal to the gut-instincts of the white working class blue collar American male by playing on his prejudices – particularly on matters such as race, alternative lifestyles and the sexual revolution. So there was a deliberate demonisation and vilification of those who were seen as ‘different’ from that red-blooded white-skinned American male ideal – they were ‘liberal hippy tree hugging dirty commie atheist bastards’ – not to be trusted, because they were ‘anti-American’ (when ‘American’ is defined by the hard right). So, basically, American christians hate atheists because their religion is really a sort of tribal nationalism, and they’ve been played for fools by right-wing politicians.
How do you get poor and middle class people to vote for tax cuts for billionaires, constant war, erosion of civil liberties, and destruction of public services? Easy, tell them that if they don’t American Jesus will cry – and then the Gays and the Foreigners and the Nasty Atheists – and all who don’t Love American Jesus will continue to shaft them. Why are they unemployed? Not because NAFTA killed the jobs, but because God angry with America for teaching evolution. It’s the ultimate ‘bait-n-switch’. So what’s the answer to the current economic crisis – the worst in American history since the Great Depression? Is it a massive public investment and job-creation programme like FDR did? No, that would be Communistic Atheism. Instead, we must appease the All-Blessing God of America – by banning pornography!
The level of cognitive dissonance must be overwhelming. Faced with that, no wonder so many American Christians act with rage and hostility to the mere presence of atheists.