How come it's acceptable for landlords to leech off of their tenants when they do nothing in return?

They are born rich. They sit back and collect rent while their tenants do all the work.Thus is the great lie of capitalism.

99%, of the time, a landlord/manager is nothing more than a person who collects rent/lease payments.  They can either be paid by the hour or live there in exchange of rent. If you really want to complain; dig out your Rental Agreement/Lease and look on the back for the name and address of the Property Owner - write them a letter of complaint.  If the Property Owner's name and address is NOT on the paperwork....go to your nearest court house, assessors office; give them the STREET ADDRESS and they will give you the name and address of the Property Owner - then write them a letter of complaint.

I would suggest trading places with your landlord for a day and you'll see that it's

rarely like that. There's administrative work to do, also periodic maintenance or 

finding / hiring reliable, honest people who can do it when a tenant has a problem.

.. And that's just the beginning

You forgot that landlords give you a place to live.

right, because having to perform upkeep on their properties is just like a vacation. /facepalm.

Landlords are business people, not parasites. They are RESPONSIBLE for the property, pay taxes, insurance, have maintenance issues--lots of things that are a lot of trouble. It's people like you who think that because they own something you don't, that they are somehow supposed to do nothing but accomodate tenants who damage their property and make problems for them. Grow up. 

If you don't like it, don't sign a lease. Nobody's forcing you. So buy your own place.

So move out, buy a tent and live in it.

Someone's jealous 😉

Try being a landlord when you have annoying tenants calling you about every little problem like the water is too hot or it's not hot enough. 

If you buy your own place, you wouldn’t need to rent. 

I'm a land lord. I lost money last year due to a heavy repair. I hope I can make something back when I sell it.