So yes, they will "unpin any site as soon as it becomes a resource drain" unless they're feeling particularly charitable - but that's exactly how it works with torrents, too! Generally you set up rules like "seed until a maximum up/down ratio is reached for that file, then don't bother", "restrict uploads to a certain maximum speed and/or certain maximum amount of data per day", that kind of thing. I figure you'd basically have an automatically-managed cache of limited size that you'd use to hold the stuff you were liking-to-pin, and stuff that was judged to be no longer worth seeding would get kicked off, as would old/unpopular content if the cache had filled up and you were shuffling in new content.
So unpinning anything that becomes a significant resource drain is also - at least in the relatively-short-to-medium-term - fully compatible with other people being willing to "like" your site to pin it, if not perpetually, than for an extended period of time.
so you're disincentivized from using the service
It's a huge oversimplification to describe people in just those terms. People are complicated and so are their motivations, and it's hard to tell in advance which new things will be successful or not.
For example, I once worked for a guy who hadn't heard of open source and, when I described the concept to him, couldn't wrap his brain around why so many people would take the time to write and maintain a bunch of software and then just give it away. This is not the work product of "evil and/or lazy" people.
We know these two things happen, consistently. We have failed to account for them in much of the foundations of the Internet - it's the assumption of benevolent cooperation. Which was great for ARPAnet, but simply doesn't work in the wild. We have 20+ years of proof.
We cannot continue to put our heads in the sand and ignore that, because for better or worse, the Internet has become a major force shaping society.
The idea that naivete translates into mental health is certainly fascinating, but I believe the colloquial translation for that is "ignorance is bliss".
I thought the last 20 years on the Internet have shown us that "humanity is noble, and good" isn't true, and we should assume "evil and/or lazy".