I got the entire SF universe mad at me for suggesting that I value a trainer who has real-life success in fitness (with a body or stats that prove it) and has successfully replicated it with clients more than a dweeb with no records that has a cert.
To your point, some people get too caught up in being "evidence based," needing research to back everything, etc. There's still a LOT of room for improvement in study design, depending on what study you read. There are also a lot of techniques out there that haven't been studied much, that definitely produce results. Until a trainee reaches a decent strength/fitness level, the only program they need is a consistent one. The only cues they need are simple ones. The only diet they need is, likewise, a lot more simple than people make it seem.
Also a lot of people arguing against you seem to be ignoring what I bolded above.
A great looking physique / “stats” tells me as much as a cert.
This is my point. Neither of those things means as much as getting results from clients does.
The only upside to a cert, in that light, is that it proves to strangers that you're not totally incompetent and have at least a basic bit of knowledge. The downside to it is that (anecdotally speaking) I have seen people with virtually zero training experience get certified and go on to have terrible coaching methods. If your cert comes alongside hands-on experiences (even if it's just weekend seminars), that's another story.
A certification is good in that it can help people who don't know much about training get into it. They just need to keep an open mind, and be a perpetual student themselves.
Before I get too rambl-y, I will just leave it at this for now:
Its not as simple as "cert-good, no cert=bad." It's just not. I think making polarized/polarizing statements about it doesn't help the discussion in a positive way. There are pros to certifications, and the main cons I can think of are that you might have to pay a bunch of money to be "taught" things you either already know or disagree with.