The same thing can be said about JS ad analytics scripts and ads. Or sites that turn the entire webpage into a JS 'web app' when it'd work fine as HTML with static images and text.
Not the same thing. JS increases the usage a bit. Badly broken JS may use a lot of CPU - but the author still has the incentive to fix it. But mining is a completely different category - it's designed to peg your CPU at 100%, because that's what's profitable.
And what's worse, for every dollar you spend on electricity for CPU-mining, you (or, in this case, someone else) receive 5 cents worth of cryptocurrency.
