Anyone who says you should be 100% honest 100% needs to apply for Gomer Pyle's old job. Such an idea is beyond naive.

(1) There are things that when asked one should not disclose even when asked, like never tell a con man where your family fortune is if they ask. Other cases are more difficult to decide but a company begging details about your warning letter/letters, even if there are none past or present, should not get this data from you even if they ask for it specifically. Why? It undermines the FAA warning letter system- see my next point, and there are things that can be off limits to employers. I can come up with more examples if you like.

(2) The FAA warning system is specifically meant to be confidential, it functions on the basis of confidentiality, and anyone including a company that attempts to undermine it is willfully flaunting FAA policy on this matter. The policy cannot be confidential if industry prods an applicant into disclosing their data using a job as the lure. They know the policy about this, and yet they willfully choose to flaunt it, and the only reason they can get away with it pilots let them. But those pilots can also say "no", you are not going to flaunt the FAA policy on this and I do not care what you want to know about me if it is something you should not have access to.