By way of explaining what I mean when I say that Catholics have not given their brains the boot, I offer first the anecdotal evidence of my own experience. Far from being the end of reason, my conversion to the Catholic Church was more like the doorway to genuine intellectual advance. I have been learning more about philosophy and its usefulness than I would have ever imagined possible. I have been forced to reconsider and abandon intellectual prejudices that I have held for as long as I can remember. I have without question prospered intellectually since my conversion, so that it is entirely clear to me that these critics simply do not know what they are talking about if these "intellectual suicide" grenades are representative of what they really believe and not mere rhetorical excess.
So much for the personal anecdotal evidence. Before we go very far, though, we need to consider a couple of things by way of laying a foundation.
In the first place, it has to be understood that when the Catholic Church proposes some dogma for belief, it is not doing so just because it seemed like a good idea at the time. The Magisterium has not plucked the articles of faith out of thin air, nor out of some grab bag of opinions that do not differ very much in their value, as if the only reason we have these dogmas and not those over there is a matter of nothing more than historical curiosity. No. The reason why the Catholic Church has proposed these dogmas for our belief is that they are true. So when she asks the Catholic to accept them, it is not the same as asking me my favorite color, nor asking me what I think of the Broncos' chances this year. It is a matter of truth, and asking someone to believe something that is true is rather different from asking him to accept an opinion. This being the case, the real intellectual suicide would be to deny the truth - to refuse to submit to it - to live as though the truth were not actually true - to think and believe as though these things were not true when in fact they are. It would be to believe a lie, and it would be to reject rationality in favor of irrationality. When we consider the question from this point of view it becomes obvious that submission to the Magisterium is the very opposite of intellectual suicide.
In the second place, we need to recognize a certain distinction: a distinction between knowing what is true, and understanding what is true. And this is where theology comes in. Theologians such as St. Thomas Aquinas have attempted to the best of their abilities to explain the doctrines of the faith - to make them intelligible to us as far as that is possible, and as far as they are able. One could say that theology is reason at the service of faith. This being the case, once again we see that the Catholic by no means surrenders his intellect at the parish door. Quite the contrary! Given a body of established truths, he is free to exert his energy in understanding them. Is that the death of reason for the Catholic? I suggest that the critic try reading and understanding the Summa Theologica (for example) to see the amazing use to which reason may be put by and for the Catholic. For myself, I can only say that reading the works of the Angelic Doctor has been an education all by itself.
All this being so...can the Catholic genuinely appreciate the work on justification of a philosopher like Dr. Koons (mentioned in the Introduction), despite what some naysayers pretend? Of course! Because to the extent that his work explains truths that we already believe, it may be truly useful to us. Certainly there are things that Catholics are obligated to believe: but we are obliged to believe them not just because someone tells us so, but because they are true (which is why the Church tells us that we must believe them). Having believed these things, however, it remains for us to understand them to the extent that we are able to do so...and that can be the work of a lifetime. Contrary to what some of our Protestant critics would say, then, we by no means turn our brains off when we become Catholics.