One way of looking at it is this. If I put 3-5% of my portfolio in BTC or a BTC ETF and can afford to have it go to zero, then I have a survivable downside with a large upside.

If the BTC bulls are right, BTC will go up 20x in the next decade. If I put 5% of my portfolio in it, my investable net worth would go 34% higher in that decade compared to 100% equities at 10%/year (46% higher compared to a more balanced portfolio going up at 7%/year).