"Secure" doesn't mean anything. A closer (though still imprecise) descriptor is the CIA triad --- confidentiality, integrity, and availability.

A confidential DNS has real value. Without it, ISPs actively monitor customers and sell analytics about usage upstream; there are other problems, but virtually every US user faces that one. It's hard to imagine wanting to trade confidentiality off.

A high-integrity DNS is a more dubious proposition. You'd obviously rather have integrity than not, ceteris paribus, but we have effective mitigating controls for DNS forgery, so you might imagine trading it off.

Availability also sounds like a no-brainer, until you remember that almost every other component of the networking stack also has availability issues. You might not want to trade anything at all to get a more highly-available DNS, if you're going to be just as susceptible to DOS attacks because the current DDoS meta is application-layer anyways.

There are a bunch of different approaches to securing the DNS, and they make different tradeoffs.

DoH focuses on confidentiality, and has bank-shot benefits to integrity (because it breaks forgery attacks from on-path attackers). Confidentiality is its primary purpose and it trades basically everything else off.

DNSSEC makes the opposite tradeoffs: it's exclusively for integrity, provides no confidentiality, and highly prioritizes availability (that's why it has elaborate authenticated denial systems).

Depending on what you want to achieve, "secure" DNS can make sense and actually get deployed and used, as DoH is, or it can make almost no sense and see almost no uptake.

Security provided by CAs is TLS Web Server Authentication (1.3.6.1.5.5.7.3.1). CAs too are exclusively for integrity, provide no confidentiality and don't prioritize availability.