Bitcoin is not about belief. I agree with TheArchaeologist and vjudeu: signature or didn't happen

If it was this easy to break a private key, many people would already have lost many coins. For instance, most exchanges have a huge hot wallet with thousands of transactions (signatures) and dozens or hundreds of BTC on them, yet somehow nobody grabs those coins. This should be proof enough that Bitcoin security is not broken.

However, if anyone's making outrageous claims without any proof, it's pretty certain they're talking horseshit.