These are all things I care about that are being sacrificed by Apple to improve one aspect I don't care about (thickness).
I'm definitely not the only one who's thinking that, as evidenced by the comment threads here.
On your opinion on RAM - I disagree. I feel like the way memory modules are psychically, they would probably be detrimental enough (thickness, keyboard, battery, maybe eventual water resistance) that it would out weight the benefits. Besides, you can get enough RAM when you buy the notebook that the amount you get will be good enough far past the date of the CPU being good enough.
On SSD though, I agree. I think with M.2, now with Gen 4 M.2 (and SFF NVMe?), Apple could and should of went to the lengths of allowing that. Even at this thinness, there is not great excuse why not. Besides, its STORAGE. It goes bad, people want to back it up, extract it, recover it, etc. Apple should not have to replace the whole logic board for that.
"The MacBook doesn't need to be thinner": The MacBook doesn't need to exist either, but I think as technology improves and things are lighter and more power efficient, the smaller the footprint will be (size and weight).
I can see the argument against a decision to shrink it down 0.001m - which is only a 6% reduction in thickness (0.001/0.0149), but if it was a 0.49m reduction, bringing it down to a thickness of 1cm, would you still hold that same opinion?
Taking this to levels of science fiction - I would love a laptop so thin you can fold it like a piece of paper and place it in your pocket. I don't need any ports if all my data is always available in some "cloud" that my laptop has free and instant access to. So thin and cheap, if I dirty it I can crumble it, toss it in recycle, and just rip open a brand new one.