There is a great story discussing arguments people make against Bitcoin (and implicitly most cryptocurrencies) citing its lack of 'intrinsic value'. I've heard this argument many times, as I suspect many here have as well. You might arm yourself with a couple of ideas from this article, or just point people directly to it.
Bitcoin ‘Has No Intrinsic Value’ But Neither Does Fiat: Opinion
The argument is easy when you compare against fiat, there is an entirely different argument when comparing against gold and other real assets. There may be a day when those same financial giants find a way to manipulate cyyptos in the markets with rules and derivatives. Good article link.