I went into detail for the rationale here.You haven't really put forth any argument for why unrealized gains should be taxed outside of the fact you want those people to be taxed more.
The high cost is a direct result of the private healthcare system. It's baked into it. Creating profit is the purpose of it, which is what keeps prices artificially high.Thus, my point about the government not actually needing more money is valid. And you can't do M4A if over half your GDP goes towards healthcare, you have to lower the cost of it for M4A to be viable solution.