It's a community of hackers passionate about the way things work. Picking it apart helps everyone understand the inputs and outputs of a system to understand how feasible it is, and what the tradeoffs are. What would you prefer, a generic "that's nice"?
As far as I can tell, the author just kinda glossed over the brine situation. Some minerals can be sold, but his solution for the excess salt was just to turbulently mix it back into the ocean, if I'm reading correctly. The sibling comments here explain why that isn't trivial (cost and wildlife impacts). I found them illuminating!
Waste brine is substantially more dense than regular seawater, so it tends to form a coherent layer that doesn't mix easily: it's why waste brine sinks to the sea-bed and spreads out in a layer.
The waste product is brine. It's an extremely salty sludge that's toxic to marine life. In the same way that fresh water is "just" diluted seawater, but pumping millions of gallons of it into a coastal ecosystem would wipe it out.
They provide some detailed and constructive thoughts. What exactly does your comment provide? Some sort of complaint which could be solved by yourself by not going into the comments or not reading theirs, hope this helps you in the future.
As far as I can tell, the author just kinda glossed over the brine situation. Some minerals can be sold, but his solution for the excess salt was just to turbulently mix it back into the ocean, if I'm reading correctly. The sibling comments here explain why that isn't trivial (cost and wildlife impacts). I found them illuminating!