Does running ads multiply your electricity costs (run your battery dry) and/or burn up your CPU?
No.
Does cryptocurrency mining do that?
Yes.
Do you see the difference now?
Running ads also dry your battery.
Do ads make your CPU run at 100% load?
Most likely not.
Yet mining scripts will do just that.
Does that mean a mining script that throttles its resource usage would be acceptable?
No, they're still using your computational resources without your (informed) consent for their own (financial) gain.
I see ads, I might not realize that the website I'm browsing is using my CPU to mine coins. If the website is upfront about using my browser to mine I don't think it's particularly unethical.
Maybe we should try to keep the discussion honest by distinguishing between ads, tracking ads, and cpu-burning cryptocoin mining.