What Google has done over the years is thwart some of the scummy SEO practices by penalizing websites that do it; a big part of current-day SEO practices are to make your website conform to web and content standards. Basically, turn it into a decent site.

There's still the black market SEO where people hire spambots to send links, but that's been thwarted / voided by just adding a nofollow to links in user generated content like comments.

but then you wouldn't do "search engine optimization", but rather proper web engineering.

SEO has become an ambigous, all encompassing term. "Proper web engineer" is now a subcategory of SEO.

Also "proper web engineering" doesn't exactly roll off the tongue.

PWE -- peewee.

The point is there's a Venn diagram where these two standards overlap.

It depends on the type of SEO. SEO includes, for instance, making sure that your page loads quickly when otherwise you wouldn’t have prioritized that. A lot of it is unethical though.

What, precisely, is "natural" about Google?

The progression towards evil as it became more of a monopoly.