Dose - How far can you take the "less is less harmful" analogy?

[Synesthesiac]

I often come across people who choose not to take research chemicals such as mephedrone and methylone due only to the fact that you have to take quite high amounts of them in comparison to most other drugs/ResearchChems. They seem fine however using drugs like MDPV, desoxypipradrol, 2c-b-fly, etc, as you dont usually push them about 5-15mg (though some people do by accident on occasions ) and so they claim the chances of them having adverse side effects in the future is far lower.

I can see some reasoning behind it, if you consume 500mg of mephedrone and theres an extra component of mephedrone that does cause a yet unknown unwanted side effect then you have consumed a lot more of it, whereas with MDPV your likely to have consumed less of any side effect and more of the desired effect due to the drastically smaller dose. But then again, the drugs you take less of are a heck of a lot stronger, and so could be causing more potential damage through their high strength profile.

How far can you take this analogy? Or is this view essentially crap?