Yes, humanity does suffer from a collective psychosis that gives us an affinity for war. People like war. They like fighting against other countries and hopefully winning. War is also good for the economy, because the government pumps large sums of money into both the public and private sectors, giving people jobs.
I do not think it is everyone in society, but there are those humans who carry within them a warrior archetype that makes them prone to want to fight. They could use this for the good and to protect others, but too often they use it for useless violence that they justify.
When it comes to war, we don't suffer from a collective psychosis that makes us more prone to battles. Human beings aren't prone to war, but some individuals are far more likely to react by waging violent wars than talking things through. This is not a collective psychosis, though. by any means.
Humanity does not suffer from a collective psychosis that gives us an affinity for war. I think war has become the accepted thing because it is not going to just go away. As long as we are alive, there will be a war fighting somewhere. I do not think humanity has a affinity for war but have come to accept it in daily life.
Not everything is metnal illness related, but we've been very ready to classify everything as such over the past 50 years. War is not psychosis - its the right of the state in order to resist the influence of outside forces. While wars can be launched for ignoble reasons, the idea of a war of protection is very real - and can end up saving lives.