That's also something we've had an awful lot of topics about, heh.  Maybe keep this discussion brief as well.

Ultimately, if Bitcoin had retained the "1 CPU = 1 Vote" concept Satoshi had, scaling would be a far simpler question.  The idea was simple.  You were either a miner or an SPV user.  And there was nothing in between.  Scaling would be simple, as miners would get paid more as blocks became larger, so it wouldn't adversely impact their costs of running a mining node.  However, mining became centralised at a rate far quicker than Satoshi had anticipated.  As such, the need for non-mining nodes became essential to keep a reasonable degree of decentralisation.  Notice how there's no mention in the whitepaper of non-miners relaying transactions or enforcing consensus rules.  They were never part of the design, but we now rely heavily upon them.  It's because of these nodes that scaling is a far more nuanced and delicate matter.  Unlike miners, there's no financial reward for running a non-mining node, but they do help to secure the network.  Ergo, making it more increasingly more costly to run something that earns no rewards is a difficult ask.