So I want you to actually THINK for a minute about what I've previously posted (I know, it's tough!)... here's a link to help you...Should leave it at that unless you need your eyes testing. If you can't make out the pixels that are almost 1mm across on a 60" FHD TV from 8 feet away your eyesight definitely needs correction. Or maybe you are one of those oddities that likes to look at pixels rather than pictures.
Now, after you clicked on the link and read (it's only a few sentences and 1 chart, so it shouldn't be too taxing), you'll see that assuming you have 20/20 vision, and assuming a viewing distance of 10 feet, you need at LEAST a 70" screen to see a difference between 4k and 1080p.
Now, the VAST majority of people don't have 70" or larger screens, yet their viewing distance is generally 8-10 feet (or more)... Tell me now, is 4k necessary?
Needless to say, 8k becomes even less useful....
Now, if you're talking about a 32" 4k MONITOR, which you typically sit a foot or so away from, that's a completely different story. But that's not what we're talking about here!
If you're one of those few people with an 80" 8K screen that you sit 5 feet away from - good for you - at least you're taking advantage of your $20,000 purchase.... but I hardly think this describes the majority...
Now, as I already posted, this doesn't mean that you shouldn't buy a 4K TV!! If you want HDR 10, Dolby Vision, etc, you don't really have a choice as to your choice of screen - they don't come in 1080p variants. This will undoubtedly be true years down the line once 8K is mainstream - if you want future goodies like "HDR 100, Dolby SuperCool" (yes, I know they don't exist, but there will be some sort of equivalent), you'll probably have no choice but to go 8K.