Personally, I think that one can post links to Amazon or other closed systems from time to time, especially when it comes to books. Yes, Lemmy is OpenSource and here are also many present who condemn Google, Amazon, Facebook, ... because of tracking, work ethics, privacy issues, etc. Still, it is the case that some authors and self publisher may not know better or even have no idea about systems outside Amazon. In addition, one should also consider that Amazon, for example, as evil as such companies may be, can be a stepping stone to more reach for aspiring authors.
If one doesn't like something, one doesn't have to comment on it, give it a bad rating or even start a riot. One can also ignore it and let the new things to those who don't have an extremist aversion to something.
Just my 2 cent.