Oh there are many different conditions that can give you a bad trip. However disrespecting the plant spirit is one of them for sure.
I did this when taking Datura lightly with a rather naive buddy of mine. We drank a cup made from half a Brugmansia flower once. Peripheral psychoactive, yet not deliriant effects. Nasty, Dark, Awkward, Dispair...are the words that come to mind. Even with such a small dose.
And I wasn't so sure about the existance of Plant Spirits before, but 2 nights after that Tea I had a VERY nasty dream where Datura's Spirit visited me and warned me to NEVER fuck with her again. It was a terrifying dream and Datura's spirit appeared to me very much like you'll hear her described in South American Native entheogenic mythology.
I believe chemical compounds in plants might actually be connected to the plant spirits. We all know Mimosa Hostilis Rootbark contains mighty amounts of NN, DMT. A funny thing to know, keeping that in mind, is that Amazon shamans that use Mimosa Hostilis religiously say that "The ancestors of their forefathers live in the roots of that Tree(Mimosa Hostilis)"
Interresting how these Forefather spirits live in Mimosa Hostilis' Roots; Just like NN, DMT crystals "Live" in Mimosa Hostilis' roots.
I wouldn't dismiss beliefs in plant spirits, just because instead you wish to have a more scientific/analytic beliefsystem.
No, Scientific knowledge and beliefs should be mixed with ancient spiritual beliefs; The truth lies in the middle of these 2.