I think you're right, not essentially because YC is a privately-funded service, but because their sense is that the majority of their users enjoy expressing their disapproval of those with whom they disagree.
The fundamental reason why you're not entitled to free speech is because HN is not public property. You can manufacture whatever kind of persecution complex you want, I don't care.
I'm not talking about a legal entitlement, hence ethos, not right. You know, just common courtesy -- the kind that resists the temptation to throw around accusations of "persecution complex". But perhaps the concept is foreign to your kind if thinking.