It's not like they're unique to any other company in this sense. Plenty of companies make plenty of products that have, for years, lead to deaths and yet they still make them. I don't see this guy's memo saying anything like "and we should ignore these issues completely and do nothing to reduce deaths;" it sounds like he is just saying more deaths = more people joining = growth. It's an empirical observation...not that I read the whole memo.
HOWEVER, Facebook trades in information. The product that the user perceives, is contact between friends and family, the exchange of information (we all know these aren't Facebook's customers and this isn't their product, but for the sake of this point). One might reasonably think this shouldn't be considered dangerous...but this is the type of product that many people trade in these days. It has become weaponized and to great effect. Facebook's primarily problem (and hell, I have been saying this for a long time: before Facebook existed, back with Myspace-c. 1997 or so), is that they are training people to be less-than-people. The algorithms that are designed to "connect" people simply create smaller and smaller bubbles of interest groups. Once you are trapped within your search-based and like-based comfy bubble of only the things and information and people that you like, anything else seems to be a threat to that bubble. Further, the distancing of real human communication, via texting, instant messaging, nerdy internet forums, puts people out of practice of dealing with those differences in the horrible chance that you might encounter another human in real life and worst of worst: that person is different than you! AHHH! This kind of stuff is a poison.
While I do think Facebook and other social media never set out to create these problems, and I think it certainly can be a useful tool, its model for success: selling your demographic information to advertisers, could only ever be a target for exploitation and human misery when given over to full, unrestrained capitalism. Algorithms don't have a soul. It's time that tech douches and optimistic futurists actually understand what that means.
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