Is it wrong to use a .org domain (as the other two of the big three
domains are sold) for a profit-making business idea (selling
educational materials).
(There could be a charitable consideration to the idea creaming off a
small percentage to charity if that helps)

drydoc...

The concept that .com is for commercial sites, while .org is for
(preferably non-profit) organizations and associations is more a
matter of convention and perception, but it is not based in fact.

There is probably no higher authority to which we can look for an
answer than the Internet Corporation For Assigned Names and Numbers
(ICANN):
http://www.icann.org/

In the midst of a rather arcane article about top level domains (TLDs)
in business, under a section titled. 'Why Not .net?' it is noted:

"Granting the original intent for the current gTLDs, THERE IS NO
 LAW OR RULE PREVENTING A COMMERCIAL ENTITY FROM USING .NET OR .ORG.
 Therefore, if John Doe Inc. wants to register a domain name for a
 commercial web site and branded email address, he might reasonably
 want johndoeinc.com.  If that name is already owned, he could
 choose johndoeinc.net or johndoeinc.org. But that is not what is
 happening. It is more likely that The John Doe Company will opt
 for some other, second choice derivative of its name in .com. The
 question is, ?Why??  Is this decision motivated by the originally
 intended meanings of .com, .org and .net? Is it because of the
 broad recognition of .com, or is it simply that the John Doe
 company has not been given a more appropriate and desirable choice?"
[emphasis added]
http://www.icann.org/tlds/biz4/BusCapPlnBizPt1.htm

They go on to explore the answers to these questions through the
exploration of the results of a research study. However, it is quite
clear that even a strictly for-profit entity is quite entitled to 
use a .org extension for their domain name.

sublime1-ga


Searches done, via Google:

"can use .org" domain
://www.google.com/search?q=%22can+use+.org%22+domain

Just what I needed...