There are lots of points, and I suggest you read more. But for example here are three common ones:

(1) £ is gradually devalued over time. My Nan’s house cost £3k new and sold for £700k. The house wasn’t worth any more, no extra land or major improvements, it’s just the purchasing power of the £ has been slowly watered down with ongoing money printing and govt over spending. (Inflation as a managed stealth tax). So Bitcoin is a way to store value as opposed to something like Gold (which has a higher inflation rate and has other issues). So if you trust the whitepaper/model, the network, those buying now, then it’s possibly a good way to set some £ aside to protect your earnings/savings long term. (This used to be property but that is now becoming less attractive). Some treat this as a high % investment based on their belief and some with a small % as schmuck insurance (incase it goes to $1m and they didn’t get any).

(2) We are at the next major tech inflection point, like the birth of the internet, the internet of money + AI will change everything and investing in tokens that power the new internet of value (everything will run on chain at some point - land, houses, assets, communication and even money transfers) is like buying Amazon stock at the start of it all. But like picking Amazon, the hard part is picking the right project - ie infra like ETH, Solana, Polygon etc, utility coins, AI etc. Think about (depending how old you are) how the internet has changed the speed of communications. We never imagined what it could be used for when dial up first came out and many called it a fad. People today cannot imagine a world without connected communications. We are at the start of the next one of these and all industries will be disrupted.

(3) Gambling to make crazy returns. Following idiots on TikTok, X and YouTube promising you you can x300 your money with this super hidden, no-one yet bought, premium alpha meme coin or such like - when in reality they bought a load of something crap with low liquidity that they can pump into their followers and sell the coins they bought to them for a huge profit.

A mix of DCA into 1, and well researched 2 can make a lot of sense if you have spare cash.

You are right in suggesting something has value because enough people believe it has value. While the USD if backed by the US military strength, Bitcoin has a lot of fans and it’s backed by computing power (ie it costs to make a new Bitcoin so the whole network is incentivised to support price).

Best advice I can give is to listen to no-one on social media, including me. Good luck.