“or” in a SPARQL query

I’m not entirely sure why you say SPARQL doesn’t supply ‘the basic logic operators’, because your own examples clearly show that it does: it provides logical-OR (||) and logical-AND (&&) as part of FILTER conditions, and disjunctive graph patterns using UNION (of course, conjunctive graph patterns need no special syntax).

Other variations of OR-like constructs are also possible. For queries of the form “this particular value must be one of these possibilities” you can use the set membership operator, IN:

SELECT * 
WHERE { 
    ?s ?p ?o.
    FILTER (?p IN (:propA, :propB, :propC ) )
}

You can also use the VALUES clause for this kind of pattern:

SELECT * 
WHERE {
    VALUES ?p { :propA :propB :propC } 
    ?s ?p ?o.
}

Update I forgot one, perhaps the simplest. For queries such as yours, where you are looking for a few alternatives for a property name, you can actually use a property path expression as well, like so:

SELECT * 
WHERE {
    ?s :propA|:propB|:propC ?o.
}