If you inherit an expensive property in your twenties, and you stop studying and live off rent, then yes, you have become an unproductive "parasite".
If, otherwise, you rent the property for a couple of years while you finish your studies and save some money for reforming it before going to live there (or sell it)... then of course you are not a parasite.
Let's say I live out of rent from my mid-30s.
In the first case, it's because my rich father died and I inherited; in the second case, it's because I worked 10 years as a highly successful professional, which allowed me to buy the property.
Am I a parasite in the first case? Am I a parasite in the second?
Variant: am I a parasite if instead of having inherited / buying property, I inherited / bought a large amount of stock in index funds and I live off market returns?
But if, at the end of your life, your contribution has been grossly negative, then I guess that you have been.
Listen, I don't even think that being a small-scale parasite is a morally horrendous thing. If you are happy, that's OK, you are not really hurting anybody. I'm just very sad that all of our cities are teeming with large-scale ones!