It seems great, until you realize that all restaurants end up buying from them and after some years they put all other farmers out of business and you have no other choice in the market. Now they can charge whatever they want, and if you are a cook who would like to use some different variety of tomato, you are kindly told to get lost.
Also, we all have to spend the rest of your lives praying that there is no new disease that can come up and affect the tomatoes sold by them.
I am not sure why this is, but I think a large part of it is that it sounds much better to rail against Facebook than to say "I don't like the outcomes when large groups of people are allowed to talk to each other online without intermediaries." But really, the second thing is what you are typically actually saying.
In my opinion facebook is very beneficial to society, so I find it strange that such a strong negative claim, stated as a fact, yet only a matter of personal opinion is left unchallenged.