Being raised in a secular, narcissistic household as a person struggling with disability and mental health issues, had mild conduct-like traits as a child, I know what it's like to live in a filter of a godless, meaningless existence. I know what it's like to realize, not over-dependency, that your not good enough because there will always be people more content, socially closer, better-looking, and smarter than you will ever be. Also, living a self-serving life as a child and teenager has lead me and some others I know who are also secular a miserable life. I am now a spiritual person, not religious, but simply spiritual.
Despite many secularism and organizations promoting self-sufficiency in the absence of a God, many who don't believe in God just can't do it. Without deep, spiritual growth, one is overly conscious of demeanors and appearances (how others perceive them), materialism, and trivial things that shouldn't matter.
The truth is, without a moral code coded by the higher intelligence or intelligence is going to fall down - we can't expect everyone or most people to be caring, loving, diligent, and ethically high in the society. Most or a lot of people, without the belief in religion, will fall away into bad behaviors, substance abuse, and even harmful behaviors to others. Cluster Bs make up 30% of the population according to some research. Those higher in psychopathy, narcissism, and mischievousness (30-40% of the population has at least some traits of these) will never learn their lessons, outside of criminal activities, on how to treat others if there is no karmic cycle and consequences.
Outside of those with serious personality disorders and mental illnesses, many do suffer from a lack of self-discipline, greed, and hostility. It is not that uncommon for people to suffer from internal resentment, jealousy, prejudice, and sadistic traits such as taunting their peers. Without feeling and believing in the infinite, vast love from a higher intelligence, some will feel treating others lovingly and being supportive without reciprocation is just pointless. Without being taught you'll be judged and unforgiven if you don't forgive others, how are many people who aren't empaths (60% of the population) going to forgive others who's wronged them. Living in a godless, materialistic world is going to create a lot of trivial competition and jealousy.
Some say religion created all or most of the wars in the world, but it doesn't always do so. When practiced in a healthy, non-corrupted way, many who are damaged psychologically/personality can be healed and fixed.