I concur that people are fooling themselves. But, really? I mean, c'mon. REALLY? You seriously expect me to believe you don't realize you are just making crap up?
Right, time for argumentum ad anecdote. Apologies in advance for the tl;dr
Despite hanging around with some pretty strange people, and naively considering myself a Charismatic long before I had a good idea of what I was identifying with (if I'd known the full story, there's a fair chance I'd have run a mile), for a long time the phenomenon of glossolalia was a closed book to me, something that I'd heard of, but which seemed intriguing but also completely wacked out. I didn't know what to think. I was happy to leave it that way, thinking that if God wanted me to talk nonsense, He could sort it out Himself. I wasn't going to load the dice or make an idiot of myself trying to make something happen.
So one day, I'm at a big summer festival. The first morning, I go along to an early morning prayer session and the guy leading it starts pushing tongues very heavily, which was nearly as bad as it sounds. I didn't like that, and especially his explicit assumption that God would just give it to anyone who wanted it - I even had Bible verses ready to back me up. At the end, after I'd sat through this for quite a while, we had a passive-aggressive Christian exchange of views, and I trudged off feeling distinctly unimpressed. I went and ranted to my girlfriend about it, letting fly with some pretty sharp words about this guy's obsession with getting people to talk nonsense, before she eventually muttered that she had the gift I'd been so forcefully eviscerating. I may have referred to "nutters".
That week was strange. Previously, I'd had no direct knowledge or experience of the phenomenon, and hadn't even realised how many people seemed to have experienced it personally. I felt unsettled, and naturally, my relationship with the GF was pretty confused, even by the standards of chaste young Christians. I was asking lots of difficult questions, and getting lots of prayer. Now, I was aware that people sometimes fell down in these situations, but I'd always thought it was a suspiciously strange thing for God to do. That week, it seemed that every time anyone prayed for me, I shook like a leaf until I literally couldn't stand. Once, I lay unable to move for what felt like an eternity. I hadn't expected it, it just happened. There would come a time when I became rather good at delivering these reactions to order, but this was genuine and inexplicable to me.
It started to feel as if a whole world I'd never been aware of was opening up for me. I didn't know what to make of it, but it felt good and everyone was treating it as entirely normal, so what could be wrong? So now we come to the final night - a feverish atmosphere, and the guy at the front starts talking about the gift of tongues. Who wants it? After the week I'd had, my suspicions had softened, I was prepared to believe in things that I'd previously dismissed, and this felt like a Biblical story of redemption, undoing my initial mistake (if that's what it was) with a final act that made everything better. So I got up and went down to the front for prayer.
The man at the front was making weird noises. I think most of the thousands of people there were doing the same. I stumbled over a few syllables, worked on them a bit longer, and finally, with some encouragement, settled into some noises that almost sounded like something. And I was delighted! I remember rushing over to my GF, telling her that I finally understood. Even though I was obviously just making up sounds, it genuinely felt real, as if I'd managed to achieve something. I don't even know now what it was that I thought I understood - maybe how it felt. Either way, it faded soon enough.
My problem, if you can call it that, was that I couldn't stop picking at things and thinking about them. As the glow faded, and that week passed into memory, it didn't feel right. I imagine a lot of people, on being told or led to believe that they have the gift of tongues, just go off and make unintelligible sounds with no difficulty and without the intrusion of their conscious brain. I tried to, and managed to make it work for a while, but in the end, I couldn't do it. I was always analysing it, which led me to doubt more and more whether any of it had been genuine. But this was just another symptom of the thing that made me difficult, the fact that I was always asking questions and looking for evidence.
After this, I found out a lot more about glossolalia. Lots of people swore by it for personal private prayer - if you didn't know what to say, you could just open your mouth and mumble away in whatever language came to hand. So it wasn't just about group dynamics. Some people didn't just get the gift all on their own out of the blue, but spent a long time hiding it from others when they were younger, because they thought it would seem weird. So it wasn't just created by expectation or environment. It seems to be moderately common, when connected to ecstatic religious experiences, and easily imitated by anyone who wants to fit in. The proportion who are truly genuine is up for debate, but I expect most people believe it to be genuine as strongly as they believe their religion of choice.
Once you've swallowed the principle, how would you test whether your utterances made any sense, however much you stumble over them? Especially once the deck's stacked by allowing the possibility of "angelic languages" that are unknown to man. Every so often, it would be normal to hear third-hand reports of some missionary speaking in tongues and being told that he was speaking the local tribe's language and the entire village had converted on the spot - entirely uncorroborated, very doubtful for many reasons, but enough support for those who want to believe, just as creationist fabrications (like the NASA/Joshua/Missing Hour one which I fell for long ago) are enough for them.
You could reasonably accuse people who claim the gift of tongues of a lack of critical thinking - in fact, it would probably be a very easy case to make - but I doubt very much that you could make the charge of dishonesty stick.
