is a relative concept.
A more precise way of looking at effects is looking at therapeutic range
. The dynamic relationship between intended effect(s) and unintended effects(s).
The claim could be made that anything is toxic, and that would be correct, but therapeutic ranges vary wildly. Water is toxic when administered at a high enough dose and over a short enough interval. THC (as in from marijuana) has a similarly broad therapeutic range, the toxicity has thus far been ineffectively measured, because it is so low. Coumadin(aka warfarin) for instance has a narrow therapeutic range, so frequent blood tests must be administered when it is used. [Walking that tightrope between bleeding out, and clotting up.
I agree that using something such as (cassia)cinnamon in moderation is not unwise. My caution is against the "magic bullet" thinking that if some is good, a lot is better. But if you love to eat a lot of cinnamon just look for ceylon (it also tastes better).
There is also some interesting new models of understanding regarding inflammation and carcinogenesis (cancer). It has long puzzled researchers why feeding patients distilled antioxidants does not convey the same benefits as eating fruits and vegetables. They have tried adding different antioxidants together (hoping for additive effects). Still no luck.
One theory regarding this (that I sympathize with) is that the benefits of fruits and vegetables is due to an interplay of toxic and anti-toxic substances within plants. Eating plants "strikes the right cords" on our immune system. They challenge the immune system while also augmenting it, but they do it in just the right tone of voice.