If a site has tons of https links leading to it, or uses HSTS, then MITMing it without a cert would not be useful. So you MITM it with Let's Encrypt, and they w

If a site has tons of https links leading to it, or uses HSTS, then MITMing it without a cert would not be useful. So you MITM it with Let's Encrypt, and they will give you a cert and you just increased your attack capabilities by leveraging Let's Encrypt. This isn't really a failing on Let's Encrypt though, because tons of other CAs issue certs by only verifying this exact same stuff. Certs are only as secure as the least secure CA. Since the security was already this weak, Let's Encrypt has not made it any weaker.