Blockchain isn't inherently a scam, Bitcoin, Litecoin, etherium, monero and others are valid ledgers. They serve their intended purpose technically. You are specifically pointing out that there are investment scans in new shitcoins that are pumped up and dumped, or that never even really exist. You are correct that this doesn't exactly happen with fiat currencies but there are still nearly identical scams, like pyramid scams where people "invest" and they see their account value go up in USD or other fiat, and every month their account balance is inflated. Some people may be able to withdraw their money at first, or maybe nobody can ever withdraw anything.

Blockchain isn't inherently a scam, pretending to launch a coin or launching a coin and abandoning it is hardly different from existing scams that are settled in USD that sell land that doesn't exist or scammers that try to get you to invest in their business and then disappear with your money. You're characterizing all Blockchain currencies as scams, it's just not true. I spent my career working in IT, I look at Blockchain as a technical invention. There are ways to transact securely on Blockchain.