He did not fit in well at Fordham, because he was not a Thomist. His philosophical background was Phenomenology, like St Edith Stein and Bl. Pope John Paul II. One of his early books, 'In Defence of Purity', strikingly anticipates many of the themes of Theology of the Body. In the 1940s, it was a common view that Catholic philosophy had to be Thomistic. Such a view is historically indefensible: however much honour the Church may, and should, accord St Thomas Aquinas, other philosophical systems and methodological approaches cannot be ruled out in advance.
In any case, he went on to be one of the great early defenders of Catholic Tradition, and founded the Roman Forum / Hildebrand Institute to carry on his work of giving a reasoned defense of the Faith in its fullness. (Dr John Rao, the Director of the Roman Forum, is giving a talk at the approaching Latin Mass Society Conference on 9th June.) Hildebrand found that many other defenders of Tradition took the same narrow-minded attitude to Catholic philosophy as his Fordham colleagues had in the 1940s. He called them 'Integrists'; I'm not sure if this is the right word but we need a label, and it'll do. It is extremely interesting to read what he has to say about them, because the Catholic traddy scene is still, and perhaps inevitably, populated by people who can be described in this way. Hildebrand examines the question of whether 'conservative extremists', 'integrists', are just as bad as the opposite, progressive extremists. He rejects it.
He goes on to give a psychological explanation for the tendency to equate the 'two extremes' among Catholics inclined towards a conservative outlook.
'Men who have had to suffer much under the narrowness of spirit of the extremists, and who have been unjustly suspected of being heretics, have developed such an antipathy toward this fanaticism, and they shun and fear it so much, that they are inclined to put this evil on the same level as grave errors of faith, or indeed as explicit heresies.' (p18)
The question of what philosophical, theological, political, indeed cultural and educational attitudes are compatible with the Faith is, of course, the question of the day, and perhaps the question of every era in the Church. There will always be people who take a broad view, and people who take a narrow view. The narrow view is the safer view; the broad view promises exciting possibilities of various kinds. If we are allowed to do this, teach that, or permit the other, we may have more tools to spread the Faith, we may be able to lift burdens off people's backs. In the end the Church makes the judgement, but only after public debate, sometimes going on for centuries. The latitudinarians think everyone else is an integrist; the integrists thinks everyone else is a latitudinarian. But Hildebrand makes the important point: however wrongheaded, even destructive, an integrist may be, he does not lack the Faith. He is always on the safer side. There is no moral equivalence between someone who thinks it is not safe to say that NFP, or evolution, or women in trousers, or liturgical innovation, is compatible with the Faith, and someone who says that you can be saved through Buddha, or denies the Real Presence, or thinks there's nothing wrong with sex outside marriage. On the one hand you have someone who is, perhaps, annoying, and if mistaken is obviously mistaken on certain (highly complex) theological questions, but he is not denying any truths of Faith. On the other hand, you have someone who clearly is denying truths of Faith, even if they claim that they are merely presenting a new interpretation of it.
What is the error of someone who holds a narrow view of what is compatible with a doctrine? In a certain, sense, he hasn't got the doctrine right, because he is drawing implications from it which it does not have. But no human, on earth, is able to see all the implications of a doctrine, they are infinite. About the implications of doctrines, we work out what we can, and await the definitive judgement of the Church, which may be a long time coming. What is required of Catholics is to believe the doctrine, in the form presented by the Church, and the integrist is doing this even if he gets some of the implications wrong. But when you hear someone saying that the truth is compatible with the denial of the doctrine in its familiar formula - Jesus isn't really God, Mary isn't really sinless, there's no original sin - they are denying the doctrine, as presented by the Church, and that is a completely different matter.