[gnfargbl]

You're absolutely correct. But: Wikipedia aren't trying to ban all multiplexed IPs. Instead, they're seeking to ban the IPs that bad actors disproportionately use -- and those are the heavily multiplexed ones.

It's kind of the internet equivalent of keeping drug dealers out of your club by banning anyone who lives in a poor area. A lazy (and likely discriminatory) policy, but a simple one, and effective.