I had almost that exact conversation with my boss a few years back (except for the part about almost getting fired). I was completely stunned that people thought I was indifferent to their ideas and bent on finding flaws, because I had actually made an effort not to do that for quite a while before the conversation. It turns out that, at least for me, navigating through people's sensitivities while having a technical discussion and making sure the truth is discovered is extremely difficult.

The effect it had on me was to basically make me clam up, because I decided that pointing out issues that would eventually crop up was not worth the risk of alienating my coworkers. It's hard for me to say whether this was a net positive or negative in terms of overall productivity, because if my shutting up makes the team more cohesive, I can see how finding the problems for themselves would grow their strengths over time. On the other hand, we often make decisions now that I would have questioned before in the process of talking it out (that includes my own decisions often enough because the whole discussion process is chilled). Ultimately, we seem to have a more congenial team (at least on the surface) at the price of having more bugfixes to deal with. Very unclear to me whether I did the right thing, but I can't really think of another way to handle it.

Edit to add:

The other big effect I noticed after learning to let stuff go was that I generally feel a lot less invested in the projects now. Before, I would treat every project I was on like it was my baby, and now I feel much more like I'm just working on somebody else's thing. That's not necessarily a bad thing (my phrasing is poor above, but I'm too tired to fix it at the moment), because it probably more accurately represents the real situation. The sense of detachment does tend to mean that I don't push as hard to go beyond expectations though.