> if Let's Encrypt has this problem, you can't trust other certificates either.
To be perfectly honest, I don't really trust the other certs, either. I mean, I pretty much have to, and having a mainstream CA sign a cert does provide a bit of reassurance -- but only a bit. I don't really consider CA signing to mean that the cert is "trustworthy", because I don't really trust those CAs, so if they're the anchor for a chain of trust, then the chain of trust is weak.