"There is a very real chance of bitcoin going to zero or otherwise so low that it will decimate any savings that were invested. You should only invest money that you can lose without remorse."
My friend replies: "I have a positive cash flow, a house and perhaps we'll keep $50000 or so in silver just in case. The rest (no matter how much it is) I can lose without it affecting our lifestyle, and that part I want to invest in bitcoin."
Your friend is forgetting the primary objective of capital/savings. It is to take care of you when you - cannot - work, due to illness, accident or old age.
Speculating with all your capital you risk losing it all and might have nothing to fall back on when you cannot work anymore.
I made a new post explaining that argument in more detail.