You're describing making fake gold, not double spending gold. Bitcoin is much better than gold for forgery protection.
I'm describing the analogous situations between gold and bitcoins. Diluting gold and spending it is analogous to a double spend in Bitcoin.
It is not. If you make a coin that is 50% gold and 50% lead and you try to deceive people into thinking it is 100% gold that is forgery, not double spending.
If you spend this fraudulent coin once the coin is then not in your physical possession anymore, therefore you cannot spend the same coin it a second time.
No you can't. Only one chain can be true at any one time. Therefore one of your two transactions in a double spend will be discovered to be invalid. You will be caught as a double spender; of course you might well have gotten away with the goods by then. Just as if you pass diluted gold you would be caught eventually.
Double spending = making a valid spend, waiting to collect its benefits, invalidating the first spend by making a double spend.
Wait a bit, repeat. You can double spend for ever since you can have as much identities as you want.
Exactly, which means they aren't spent any more. In the end a double spend will turn into a single spend. Even someone with 51% of the hash power has to pick one chain or another as "true".
Of course, thats pretty obvious, it doesn't change the fact that at that point you will have spent the *same* coins twice (spend = give coins in exchange for a valuable benefit).
Unless of course they are abusing that privilege to make loads of orphan chains while they double spend, in which case the remaining 49% will see it. If they aren't doing that, then no one will care as they are an honest miner.
Yes, unless you do it smartly and combine that with isolating nodes. We do agree that it's very unlikely/impractical.
Depends what properties you want. I've never had the urge to hold gold, but I do hold bitcoins.
The only one you've mentioned that falls in gold's favour is that has some history to it. We might perhaps add that the current price volatility makes day-to-day use a little, shall we say, "nervewracking". Other than that, as far as I can tell, Bitcoin wins on every point.
You fail to see the obvious "acceptance" point, bitcoin has the potential to be much better than gold as a currency, but as of today you're much more likely to get gold accepted as a payment in exchange for whatever good/service you randomly pick on the surface of the earth, if you fail to see this simple truth you're deluding yourself.