It's not really a trap -- it's more a rhetorical tactic.
The trick is that when you say "I used to believe X, but now I've realized I was wrong and believe Y", you can get away without giving evidence for why X was wrong and Y is right. You appeal to a commonality between you and your audience (your audience believes X, you used to believe X) and by presenting your change you imply that they are being left behind, that they have missed something you have seen.
It's such an effective rhetorical tactic that speakers will sometimes make up a conversion experience to use in their evangelism, even if they have always been a member of the faith.
There's nothing wrong with changing your mind, with adapting to new evidence. But you shouldn't confuse someone's declaration that they have changed their mind with evidence for the position they have adopted; that's where logic and rhetoric diverge.
(And again, I'm not trying to start something with the GP; I am fascinated by the universal utility of the rhetorical device more than this specific case.)
Late to the party but FWIW I used to be an atheist and then a Buddhist and am now a Christian...
My attitude is very different from the evangelist’s, it says “look that was an important part of my journey and if that’s the direction you’re going, don’t let me dissuade you. I can tell you why those didn’t work for me but I can’t hold up my present consciousness as “the only correct thing, believe as I do or else you are irrational or anything like that. Heck I am sure that we are both irrational in innumerable ways and why would I pretend I’m more sane than you?”
This fatalism also infects a lot of how I teach things like physics, I tell people a lot that “learning is pain—or more precisely, learning abstractions relieves a pain and chaos and difficulty such that you can only truly absorb the abstraction when you have felt the confusion it addresses. So I can no longer pretend that ‘now that I have suffered through all of that, here is the Right Perspective so that you don't have to!!’... I’d have to take you through the suffering to get to the teaching on the other side.”
I'm sorry, but I will do this: I used to think like you're thinking. Pointing other people's logic fallacies, understanding sophism and the logical soundness of arguments.
Logic, for human debates, is very nice in theory. But there is a reason humans adopted shortcut thinking and don't use logic all the time. We are not robots. We don't have infinite processing capacity, and statistics and probability save A LOT of time. For example, doing strawmen fallacies is useful. It allows you to filter through a lot of crap before investing time in digesting whether what that person said makes sense or not. If you would go into any conversation with a blank state of "Let's analyse the logic here" Good luck with that.
So we adopt shortcuts. What shortcut is he doing? "I'm like you" is indeed establishing commonality. The person is saying "I get where you're coming from, i've been there, so I understand at least some reasons why you currently think that way." This is useful if the person is being honest because it let's you know that this person might be saying something more valid than if they had no idea where you're coming from. It means they were once in your position, and something made them switch. It's different than if they never had been in your position. They never had to think anything through. So knowing this is useful. This saves time. Is it fool-proof? Not really. People can lie, or might have not thought that much about it anyway, but like I said people are not robots, and we can't analyse each argument like if we were one.
So rather, let me also help make a shortcut and your argument more clear: Don't call out this behavior, which from an honest person is good, call out what you're actually thinking that he's doing - that he's trying to manipulate readers. Why you would think that, I don't know.
The trick is that when you say "I used to believe X, but now I've realized I was wrong and believe Y", you can get away without giving evidence for why X was wrong and Y is right. You appeal to a commonality between you and your audience (your audience believes X, you used to believe X) and by presenting your change you imply that they are being left behind, that they have missed something you have seen.
It's such an effective rhetorical tactic that speakers will sometimes make up a conversion experience to use in their evangelism, even if they have always been a member of the faith.
There's nothing wrong with changing your mind, with adapting to new evidence. But you shouldn't confuse someone's declaration that they have changed their mind with evidence for the position they have adopted; that's where logic and rhetoric diverge.
(And again, I'm not trying to start something with the GP; I am fascinated by the universal utility of the rhetorical device more than this specific case.)