@Sci
About imperialism:
If "the Federation is engaged in a systematic campaign to erase cultural beliefs that do not mach its beliefs through
persuasion" then the Federation is NOT imperialistic.
As per the
definition (quoted by you), "imperialism"
requires systematic political or
military pressure against another civilization in order to change its values.
Mere persuasion is cultural imperialism - at most.
About cultural imperialism:
Ferengi and Federation civilizations - at first, each civilization rejected the other's values out of hand. And each civilization tried to persuade the other one of its values every time they met.
In the end, the Federation persuaded the Ferengi to adopt some of its values and not the other way around.
Why? We can speculate that Federation values give birth to a civilization which creates happy and productive lives for the largest part of its population - unlike traditional Ferengi values, for example.
Whatever the reason, what is important to realise is that the Federation used ONLY PERSUASION (backed up by NO PRESSURE WHATSOEVER) to spread its values. Much like the Ferengi used persuasion to spread their values.
This is called '
exchange of ideas' - and, as I already mentioned, it is not only
inevitable when two civilizations meet, but beneficial to both civilizations.
I have the impresion that this 'exchange of ideas' is not what you actually criticise - you don't like the fact that this 'exchange of ideas' is SO EFFICIENT in spreading Federation values.
Well, Sci, perhaps Federation values just make sense

.
Sci, I am surprised that you argue that the Federationn is culturally imperialistic.
The scenarists/writers specifically made the Federation to be as culturally NON-imperialistic as possible - and the Prime Directive is the clearest proof. They made the Federation so NON culturally-imperialistic that the Federation often looks suicidal or plain immoral.
I know you disagree - in this case, Sci, create an hypothetical STABLE civilization that travels between stars and talks with other species/civilizations which is actually LESS culturally imperialistic than the Federation.