I'll try, even though I'm also still wrapping my head around it.
> It's a bad currency because it is slow to exchange and costs lots of money to exchange - I can't use it to buy my coffee in the morning.
I'd say that there are 2 ways to address this:
1. Bitcoin is less analogous to cash or credit cards, and more analogous to the US dollar. Today, when you buy a cup of coffee with a credit card, your issuing processor updates a database entry reflecting that you owe the coffeeshop $X. At the end of the day, the issuing processor submits a batch file to a network of automated clearing houses to reflect this movement of money. This process is extremely asynchronous, and can take up to weeks to complete. Processing a Bitcoin transaction on the blockchain is analogous to that very slow, very asynchronous process.
2. Bitcoin is about as "bad" a currency as gold is. It's fairly impractical to pay for a cup of coffee with gold, unless you are able to carry a pile of it that's cut into small enough pieces that you can reasonably transact for cheap items like coffee. A crypto bull would tell you that if your use case is to buy a cup of coffee, you're better off using a credit card through a trusted network, where the currency that's being transacted is BTC or ETH instead of USD, JPY, EUR, GBP, etc. The reason why you would have a trusted bank account storing BTC or ETH instead of USD etc is because it lets you opt-out of being at the behest of a central bank that might co-opt a monetary policy you don't agree with — or worse, can render your currency useless if they do the wrong thing. It also lets you digitally transact with people in a trust-less way if you really need to. That is to say: you don't use Bitcoin to buy a cup of coffee, you use it to pay for porn on PornHub or OnlyFans because those companies have blocked by the major payment networks. Right now the only way to pay for stuff like that is by withdrawing cash and mailing briefcases of it.
> It's a bad non-speculative asset, because it can't produce anything to deliver returns.
It produces one, and only one thing, and that's trustless transactions. As long as there is a market need for this, it has some use, even if it's a niche use-case.
> And if the answer to the question 'what can i do with a bitcoin?' is 'Wait until it is valuable, and then you can turn it into a currency you can actually spend' then it's not actually fulfilling what it set out to achieve.
I think this is a good criticism, but is one that a bull might argue will hold less true over time. In the bull's perfect world, there exists enough tooling and frameworks to allow someone to live their entire life off of Bitcoin while still interoperating with the tradition financial systems seamlessly.