for me, the most dangerous thing about dmt is psychological/spiritual aspect. One could, for instance, have a terrorizing haunting emotionally scarring trip off the deep end. On the other hand, one might get absorbed in the dmt consciousness and get lost in the mystique of Dmt.
In the past I used lots of rc's a lot. I was slightly addicted to psychedelics for a while. It was a pretty interesting time in my life, but after a while I just felt like I was too "out there" all the time. That would have to be one of the more harmful effects I experienced from using psychedelics. Don't even get me started on ketamine.