It may be an investment, but for every seller there needs to be a buyer. There's a direct 1:1 relationship. For everyone who bought at $100 and sold at $20,000 there was someone who bought at $20,000 and is sitting on incredible losses.
And it may be an investment, but what are you buying? This is a serious question. What are you investing in that give the BTC value? No product or service is created to add that value. It's more akin (right now) to trading baseball cards and beanie babies than AAPL and XON or even traditional currency trading.
People can sink as much money as they want to into it - I don't care - but to say it's a currency that is better than what we have is a lie. Why not use gold, or silver, or diamonds, or rubies, or whatever else isn't fiat currency to trade? No one controls those prices, either. The simple fact is you trust some decentralized system from across the globe to not just suddenly create more BTC and drop the value like a rock. Sure, that *could* happen with the Fed, but at least we can vote in a new congress to deal with it.