Pointing out that someone who is not an expert in a particular field is not an expert in that field is not 'ad hominem'. That is a 'true statement'.

When you have a complicated system, and a non-expert comes in with a plan, then it's appropriate to dismiss it without overwhelming support. The burden of proof is on the non-expert. Expert time is too valuable to waste debunking every hobbyist solution.

You see this on a small scale in mathematics, with professors getting incorrect (and frequently laughable) 'proofs' or outstanding unsolved problems or problems that have been proven not to have solutions.