Bitcoin-in-personal-wallet is to gold as Bitcoin-on-exchange is to gold-certificate.

I agree.

Bitcoin is "unbacked" in the same way that gold is "unbacked" -- they are themselves the commodity used for backing.

Disagree. Gold has both uses in industry for which no other element is suitable and sentimental uses and traditions extending back milennia. Bitcoin has no use (independent of its utility as a currency which a gold-backed cryptocurrency also achieves).

Gold certificates are not comparable with Bitcoin. They're subject to counterparty risk. Personally held bitcoin is not (just as personally held gold is not).

I agree with your point that gold certificates are subject to counter-party risk whereas Bitcoin isn't, however a cryptocurrency backed by gold is, like Bitcoin, not subject to counter-party risk whereas the connection between the cryptocurrency and its gold backing is. That is, even if a gold backed currency loses its gold backing, it is still as usable as Bitcoin as the tokens, regardless of whether they are still backed by a commodity, are still owned by someone.

Gold can not be sent over the internet; gold cannot be easily divided; gold's purity cannot be easily verified; gold is hard to physically secure, bitcoin (with care) can be secured by anyone willing to follow a few simple precautions; gold cannot be subject to a smart contract (N of M type escrow for example); gold cannot be transported across a border without risk of confiscation. These are all applications of bitcoin that "gold can't fulfill".

But a gold baced cryptocurrency can achieve all these. So long as the cryptocurrency can be redeemed for actual gold, there's no issue. As you've stated the issue is whether the backing is real or could be revoked but, as I've outlined above, a gold-backed cryptocurrency which is no longer gold-backed would still have the same utility as Bitcoin.

If you wanted to ship me a billion dollars worth of gold (not gold certificates, which are not the same), it would be a logistical nightmare. Sending me billions of dollars worth of bitcoin is trivial.

I could sell you a billion dollars worth of a gold-backed cryptocurrency that you could redeem for actual gold locally. Has the benefits of being sent internationally, like Bitcoin, with the benefits of being redeemable for gold. It'd be as trivial as sending Bitcoin.

The difference of opinion seems to be that you don't accept the idea of a redeemable certificate whereas I do. I agree with your point ideologically, but in practice it wouldn't make much difference so long as you cashed out quickly. The benefit being that, once you've got the physical gold, it has a higher intrinsic value than Bitcoin.