Well It depends where you're diving. It's definetly harder to dive deep without any weights in a salty sea. Baltic Sea, for example, has a quite low salt-level so diving without weights is easier - same goes for diving in freshwater (lakes). You can't say that for Caribbean and probably for most other seas.
I'd like to see someone freediving without weights in Black Sea
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More dangerous? I'd say yes, especially without a computer.
I bet freediving roots go back to pearl hunting - pearl hunters didn't use anything (duh), but dove quite deep nevertheless. Hmm... I'll see what I can find in google.
