Even though somebody else knows that you own that address, they cannot see what is inside that address. You can send money from that address to another address. That would make it unlinkable.
Yes that is correct. I think what he meant was something like: If you have your public address on your web site (along with your name) and use that same address for an (otherwise anonymous) exchange, then the exchange account can then be linked to you, not through the blockchain, but through the exchange's own records of your address matching the address on your website.
I'm for making software where even the laziest user benefits. This issue may ultimately become a matter of semantics, of course; I don't know the full design trajectory of Monero. All I'm saying is that this component of the reasoning that we have against people reusing addresses in cryptocurrencies still pertains to Monero. While Monero doesn't have the primary issue to avoid, that is, where people are able to check someone's balance and transaction history at any publicly disclosed address, Monero still runs into the problem of someone's identifiable information contained in third party databases being cross referenced, whenever or wherever it is that they've reused their Monero address.
Therefore, it seems that there is still an important usage case for having the software make effortless the management of multiple Monero addresses (or accounts, if you prefer). While Monero seems to get rid of the need to generate and manage a new address for every single transaction, there is still a need to generate and manage new addresses for each privacy case where external cross-referencing might be plausible.
I don't doubt that there are smarter people who have already thought through all of this, but it does seem to be a usage case that hasn't been fully fleshed out from a practical standpoint in the software (and please correct me if I'm wrong). It seems to currently be a clumsy situation to manage multiple Monero accounts. Each requires its own instance of the wallet software to be running, and each requires its own backup mnemonic. All I'm interested in here is achieving the maximum security that we can in the least tedious way possible for users.