Litrium: all SWIM's experiences with entities so far have been positive. Perhaps this is to do with his attitude: he goes in with respect, humility and passivity and treats all other beings he meets as equals. He doesn't judge them on whether or not he finds their appearance beautiful or not... in fact he finds them all beautiful, however bizarre. He shows no prejudice. They at the very least reciprocate, but more often shower him with love. The experiences inspire him to become a better person, and cured the depression that led him to DMT, so hyperspace is doing him nothing but good right now.
Please don't take offence against this suggestion because none is intended: maybe it's your attitude that is causing these negative occurences? SWIM doesn't believe in negative superstition like astral darts or malevolent beings etc, and has never experienced this... perhaps exactly because he doesn't believe in it.
Or maybe SWIM has just been lucky and has it coming. If disturbing stuff starts happening, he'll just stop taking it, because it will no longer be useful to him. He will keep you posted. He's entered hyperspace about 30 times so far. Do some people have these disturbing experiences from the start, or do they only start happening after 50/100/1000 trips?
As for the shamen, one poster has already posted that McKenna DID smoke it with shamen (and another said he did so with a Buddhist monk) so if this is true then your argument is plain wrong. And if there are some shaman who refuse to smoke it, it hasn't yet been proposed that their reasons could be very human ones. I'm not saying these are true reasons, but am merely proposing food for thought... firstly, they consider themselves experts in what they know, but they are not experts in freebase DMT. Often an expert will stick to what they know and warn people against something that they have no 'authority' in, especially when they perceive their lack of authority in that area as a personal threat to their status and beliefs. On a larger scale, this is a bit like how many religions claim to be the right one and denounce others as wrong. Shamen may also want to maintain their traditional ways because there is a perception of authority in tradition (among other less egotistical reasons, of course). I'm not attacking shamen, I'm just saying that they're people too, so these reasons are a possibility if a shaman were to be against freebase DMT.