There are already a lot of IDO platforms nowadays that don't need KYC anymore. Try to dive into Solana, there are some platforms there that don't need KYC anymore, for example, is Raydium platform. And also in Ethereum, have you heard DAO Maker (https://daomaker.com/)? I haven't yet tried this but I can always hear about this platform.
This is not a total red flag. It depends on the project that doing it. Polkastarter is the most trusted launchpad I Polkadot ecosystem. I agree that there method is unusual but they apply only this KYC to all whitelisted participants just to ensure that they are following the regulation incase regulators knock on there door to check there token sales.
Me myself is not a fan of KYC but due to the possible high profit of being whitelisted and purchase cheap token. People are force to comply. You can read more here: