Sure, if you want research papers claiming so, there are plenty. This one finds a negative correlation with partner violence: https://pubmed.ncbi.nlm.nih.gov/29807492
It's social science though, of course it's easy to find papers making all sorts of claim. And it also very much depends on our definition of "nice", which is a completely subjective term. My intention wasn't to claim that psychedelics make people nice anyway. Rather at high enough doses they make people reflect deeply about themselves, the universe and everything. And they look at it from a different perspective than they usually do, because the drug changes how we perceive everything.
The following is my personal view now: I think the majority of people are good and they don't want to intentionally cause great harm. However depending on their upbringing and experiences, they can easily arrive at situations where they do evil things, sometimes because they don't know any better and sometimes because they were lead to believe it's ok, or even the right thing to do. When mass psychology and peer pressure is involved it gets even more complicated, and someone might come to find actions acceptable they otherwise never would. A psychedelic user gets ripped out of this whole dynamic. They view things from an outsider's perspective, if you will. I certainly do not mean to say it makes people nicer in the long term. But, to put it this way, I have a hard time imagining soldiers on LSD running concentration camps, or peyote users burning a whole continent's irretrievable cultural heritage. That's just not the kind of thing people tend to feel like doing during or even after trips. And I want to stress I don't think it's something most people would ever feel like doing if they weren't brainwashed into aggression and hatred, or arrived at such a point through a chain of unfortunate events. Racism, nationalism, religious indoctrination, violent behavior, etc... these are all learned ideas and they can be unlearned. There isn't even a need to take drugs, but psychedelic drugs can be a way to get there.
This one claims psychedelic drug users are more egalitarian and less likely to hold authoritarian views than non users: https://www.tandfonline.com/doi/abs/10.1080/02791072.2017.13...
It's social science though, of course it's easy to find papers making all sorts of claim. And it also very much depends on our definition of "nice", which is a completely subjective term. My intention wasn't to claim that psychedelics make people nice anyway. Rather at high enough doses they make people reflect deeply about themselves, the universe and everything. And they look at it from a different perspective than they usually do, because the drug changes how we perceive everything.
The following is my personal view now: I think the majority of people are good and they don't want to intentionally cause great harm. However depending on their upbringing and experiences, they can easily arrive at situations where they do evil things, sometimes because they don't know any better and sometimes because they were lead to believe it's ok, or even the right thing to do. When mass psychology and peer pressure is involved it gets even more complicated, and someone might come to find actions acceptable they otherwise never would. A psychedelic user gets ripped out of this whole dynamic. They view things from an outsider's perspective, if you will. I certainly do not mean to say it makes people nicer in the long term. But, to put it this way, I have a hard time imagining soldiers on LSD running concentration camps, or peyote users burning a whole continent's irretrievable cultural heritage. That's just not the kind of thing people tend to feel like doing during or even after trips. And I want to stress I don't think it's something most people would ever feel like doing if they weren't brainwashed into aggression and hatred, or arrived at such a point through a chain of unfortunate events. Racism, nationalism, religious indoctrination, violent behavior, etc... these are all learned ideas and they can be unlearned. There isn't even a need to take drugs, but psychedelic drugs can be a way to get there.