There are many other false religions with natural virtues and natural truth in them.  ...
I think that before modernism all religions, though man-made, had some respect for human dignity, the laws of nature and morality. ...

   
I think we've to separate the false pre-christian religions from the false ones afterwards, like the horrible Islam. Still your words in a general sense are reminiscent of what Bishop Williamson said last year. If we remember how close the ties are between your mentioned modernism and the liberalism. Bold by me:  

Eleison Comments CCIII (June 4, 2011): Reading Pagans

[..] Now whereas for Catholics Providence is inseparable from God, the Greeks separate Zeus from Fate so that they sometimes clash. That follows from the Greeks having a too human concept of their gods. Nevertheless they do conceive of Zeus as more or less benignly directing the universe and of Fate as being unchangeable, as is Providence within the true God (Summa Ia, 23, 8; 116,3), so that they are not wholly wrong. Moreover they have more respect for their mythical gods, and for the moral order guarded by them, than do a host of modern writers, who have no respect for any god at all, and who set out to negate any trace of a moral order.

[..] so the ancient Greeks give special witness to God and his Providence when, independently of the Catechism, they demonstrate the world's moral order in action. In this way they prove that such natural truths are accessible not only to believers, rather they belong to the very fabric of life as lived by everyone, if only it is sanely understood.

Another advantage of the ancient classics in particular is that having preceded Christ, there cannot be in them a trace of that apostasy which mars, more or less, even pious writers coming out of Christendom after the Middle Ages. Natural truths are presented by the ancients with a certain innocence and freshness which can no longer be recovered. The waters are too muddied.

In fact it was the Church's monasteries which ensured the survival of the manuscripts of the ancient classics in medieval times. Count on the true Catholic Church to save them once more in modern times from the new barbarians, liberals! Wherever the so-called „scholarship“ of the liberals prevails today, it turns all classics to dust. Kyrie eleison.

...so no, I won't be quoting the Koran anytime soon.

If you kiss it publicly, however, you just might qualify for sainthood.