Though I usually dislike animal-commoner analogies, it will work here. Many modern people support rules against animal cruelty, probably most modern people. Not all modern people believe in animal rights (exhibit 1: me). It is common to believe in rules of behavior and treatment even in regards to entities we do not regard as having fundamental rights.
Though I'd argue many consider them as indeed having "rights", though most people don't affirm they have the same rights as us.
It's almost getting a debate of semantics... One can have "rights" without having all of the rights another person/entity enjoys. For example, many people consider that we do not have the "right" to chose on another's life or death, that such a thing belongs to God (i.e. another (superior) entity).
And let's not forget that freemen, by definition, are not owned by nobles. Also, if some of them got REALLY rich back in the days, it's certainly not in a context where they have no rights.
