Criticism #5: Bitcoin is not backed by anything.
Response: Bitcoin is not backed by cash flows, industrial utility, or decree. It is backed by code and the consensus that exists among its key stakeholders.
Probably the most popular criticism I've just heard from the adepts of traditional finance. Bitcoin is backed by key stakeholders, including miners, validators, nodes, developers. Interested parties choose Bitcoin because of its unique characteristics, such as scarcity, irreversibility of transactions, and resistance to hacking.
I'd like to add something to that. People, those who criticize bitcoin and claim it is not backed by anything, usually fail to recognize the difference between sound and unsound money. They think of bitcoin as an inferior alternative to fiat money; bitcoin, according to them, is worse than fiat money because governments refuse to support it and accept as a means of payment on their territories. Bitcoin is backed neither by governments, businesses, nor gold. The truth is bitcoin shouldn't necessarily be backed by something: it exists on its own like gold, which is also backed by "nothing".
Both gold and bitcoin, sound money, have proven the credibility of their monetary properties and, in effect, are backed by them. The former has existed for thousands of years and people are always ready to accept gold because they know it is valuable. The latter has existed for more than a decade, its monetary properties are set in stone, programmed; people all over the world are working hard to sustain these properties because they know bitcoin is also valuable.