well, I hate to say it but you're wrong. its been tested etc. in WSH, COL & BC to the point of knowing exactly what is in your product. there are far more things you shouldnt be smoking in the plant matter than in the extract concentrate.
there are also extracts that dont use any butane to get the substance out of the plant....and to me, they taste the exact same.
purging definition:
a. To clear (a container or space, for example) of something unclean or unwanted: purge a water pipe of air.
b. To remove or eliminate (unwanted physical matter)
so even by definition, its clean.