I think this is a complicated discussion because there are different types of danger associated with research chemicals. Plus the whole danger of consuming something with little history of use, who knows if there are long term health consequences with any of these chems.
Aside from that, some thoughts...
The "bathsalt" type drugs like MDPV can be used responsibly but they are dangerous because often they lead to very irresponsible use (high doses, constant redosing, ignoring sleep/food, etc).
The fentanyl drugs can be used responsibly but often the layman is not fully prepared to do so due to such high potency. With research and proper preparation they can be used somewhat safely with something like volumetric dosing. They are still dangerous though because accidents can always happen plus the margin between a recreational dose and a lethal dose is much narrower than with traditional opioids.
Then you have the research cannabinoids. These are dangerous for numerous reasons: addiction potential, insane potency plus some of the newer ones are possibly posing health hazards to users. I'd say the older cannabinoids can be used responsibly with proper handling while many of the newer ones shouldn't be touched with a ten foot pole.