Writersoul,
You hit upon, but for some reason dismissed, the continuation of my analogy. Yes, there can be proper use for certain drugs, and when necessary, one must learn the proper way to administer them. There are other drugs besides marijuana which have both positive and destructive uses; steroids and narcotics come to mind.
Should we educate our children how to administer these drugs because they have potential benefits?
I’ve unfortunately seen the destruction internet addiction has wreaked on individuals and families (and the rabbonim who were involved in the asifa have seen it a great deal more than I), and I’m not willing to concede that the benefits outweigh the danger.
I can’t address the use of Facebook for business purposes, since I don’t understand it, but an adult using it merely for business is likely different than it being used socially.