Anyone can use my laptop and "have" the same IP as myself.
In truth, nobody "has" an IP address. A computer has an IP address. Who can tell who is using a particular computer at a given time just by looking at an IP address?
In that sense an IP address is a way, way more tenuous connection to a physical person than a description of (apparent) race and gender.
No, it's not - one example the article lists is a Tor exit node.
In residential settings, there's a collation that whoever owns the router is likely to own the devices on the LAN - but there are also enough cases where this isn't true. Hotels, universities, cafes. Also, Tor exit nodes or people with compromised Wifi. I'm sure it's possible to come up with more scenarios. As for a statistical probability, no idea. Is 80% or 95% acceptable? I think that's EFF's argument, that there's still enough room for error.
There's only just under 4.3 Billion IPv4 addresses available. And you can write off a decent chunk of those as being not available for public use.
As of right now there are only 891 listed Tor Exit nodes.[1]
https://metrics.torproject.org/userstats-relay-country.html
http://www.foxnews.com/tech/2012/06/06/internet-grows-by-tri...
I am indeed guilty of ignoring details when indifferent.
That's an absurd analogy. An IP address isn't perfect, but it's far more specific than knowing the perp is an "asian male." What's the size of the universe of people who might have had the same IP address over a given period of time? A few?