I think I have a theory, they're assuming other people are just as incapable of empathy or sympathy as they are, therefore the only reason in their mind that anyone would have an issue with it is jealousy.

Add into that the insecure need to make other people feel bad, and they think by loudly proclaiming it for all to hear, assuming that you will feel bad upon hearing their opinion.

So long story short: they're a piece of shit and their opinions should be ignored by all.