Do websites need ads, or is there another method for their site to be run?

[Nama-Shhh]

I'm a casual member of this socialist page on Facebook and a more recent post promoted AdBlock, saying " If everyone did this, no greedy capitalist could exploit the internet to make a profit off of ads anymore!" This made me wonder if websites even actually need these advertisements or not. The only alternative I can think of is what the founder of Wikipedia does, which is take donations and are said to be non-profit. So why do some websites use ads? Can they not support the site otherwise? Are they being bribed by capitalists? Keep in mind I'm not politically savvy at all, just curious about this subject regarding how and why ads exist on the internet and spit-balling reasons.