Evolution is a touchy subject, even among Catholics. Generally speaking though, traditional Catholics are against Evolution, and I'd like to talk about why I think this is so. And while Evolution can be a loose concept, I think the following 'blanket approach' is more or less fair.
The first reason is that Evolution originated as a way of explaining the origins of life from a purely atheistic-materialistic standpoint. In other words, there is a philosophy behind evolution, and that philosophy is that of atheistic materialism, the belief that everything can be explained without any reference to God. This is precisely why science is largely dominated by atheist-materialists. This isn't an accident, and it's not lost on traditionalists who are well aware about the link between bad philosophy and bad lifestyles.
The second reason is that Evolution is taken as a secular dogmas that all are required to believe in. I use the term "dogma" on purpose, because Evolution is held as so important that if one were to even question it (even if they don't deny it), they are viciously attacked and slandered. You cannot get a job in certain fields, especially teaching on the university level, if you have any doubts about evolution. In many places, you're forced to learn it in schools, in the form they want it presented. If you deny evolution, you're slandered with the worst name calling and treated as a piece of ignorant garbage. This is taken by traditionalists as highly suspicious, since the truth doesn't need such force, and such an approach is usually a sign that some sinister agenda is taking place.
The third reason is that Evolution isn't even a specific and sturdy of a thesis, but rather contains many unanswered questions, both on the philosophical and experimental level. There aren't any specific explanations for how and why Evolution takes place, only that it must be so. There are no plain experiments that the average student can even engage in to witness evolution taking place, nor is there any way to verify astronomical numbers that are spit out by equations and instruments. When it comes to examining history, things become more and more speculative and uncertain the further you go back, and after a certain window of a few thousand years, one really cannot say much with confidence. Thus, traditionalists would view Evolution as more of a pseudo-science, masquerading as a open-and-shut case.
The fourth reason is that the Church has yet to give any stamp of approval on Evolution. The closest thing the Church has come to an official statement on Evolution is in a 60 year old Encyclical by Pope Pius XII called Humani Generis (On Human Origins), where the Magisterium said Evolution was by no means a given. All that the Pope said is that in the realm of scholarly debate, it is permissible to explore Evolution as a theory, and weigh its merits and demerits as objectively as possible (paragraph 36). In fact, Pius made it clear: "Some however, rashly transgress this liberty of discussion, when they act as if the origin of the human body from pre-existing and living matter were already completely certain and proved by the facts which have been discovered up to now and by reasoning on those facts." As any faithful Catholic should do, traditionalists have simply said we must carefully follow the Magisterium on this matter, and not go beyond it, especially not in the rash manner that many Catholics have done, treating evolution as a completely settled matter for Catholics.
Some might ask: What about theistic Evolution? So called theistic Evolution teaches that God providentially guided the evolutionary process, and thus one need not be atheist to believe in evolution. This is implausible in my opinion for a variety of reasons. Recall that Evolution is founded upon the idea that what we see today came about as a result of billions of years of failed mutations and mass extinctions. Evolution teaches that fully 99.9% of every species that has ever existed has become extinct. So what does that make us? From the atheist point of view, we're a random accident, and that's the most logical thing to say given the premises. This is why so many of these men are also Nihilists, who see life as having no meaning, since we're just one (temporary) successful mutation. Given that, a theistic Evolutionist has to have the nerve to say that an all Providential God had to rely on billions of years of failed mutations and extinction of 99.9% of creation to eventually come around to His crowning achievement. As an analogy, it's as if someone wrote a massive 1000 page book and yet only the last sentence of the entire book (i.e. when man finally arrives on the scene) was relevant to the main issue (i.e. Salvation history). It really sounds quite silly, which is why those advocating theistic Evolution are never taken seriously by the atheistic science community at large. Rather, the atheistic scientific community sees these folks as poor confused and inconsistent individuals rather than robust academic thinkers.
Solid Catholic theologians like professor Lawrence Feingold (an atheist to Catholic convert), has given a nice lecture on why he doesn't believe in Evolution (along with a Q&A session). One primary argument he gives is the fact that the way man's body is constituted, man's body is uniquely suited only for a being with the capacity of rational thought, which animals don't have. For example, man is born naked, as opposed to having something like a fur coat, because man can chose to end up living in any environment, rather than being restricted to either hot (no fur), moderate (some fur), or cold climates (a large coat of fur). Another example is man's hands, which are his primary means of survival, by which he can use to build all kinds of tools and such. The use of hands for survival only is possible for a rational being, because the being must be able to envision the concept of tools and formulate plans on how to go about achieving his desired ends. This is why man can build anything from a modest hut all the way up to a sky scraper. This would be impossible for an pre-human species that had hands but lacked the use of reason, because the animal wouldn't be able to make proper use of hands.
On top of that, the notion that God's crowning earthly achievement was conceived in a non-human being, and was nursed and raised by that same non-human beast, is simply preposterous. It degrades everything about the fact man is superior to the animals. This is why Adam is depicted in Genesis as being created as an adult, since as a baby he would have been entirely helpless and not have reached the age of reason until at least 8 years old. So that's a huge strike against the theistic evolutionary idea that man evolved. Rather, that's a story more akin to the Jungle Book, where a human was raised by apes.
I personally am against Evolution for a variety of reasons, all encompassed above. I think Evolution gives away the farm by ceding too much ground to the atheist-materialist end, all for fear of being labeled "stupid" by the establishment. I don't mind being called stupid, but what I do mind is ceding to bad philosophy and dubious science out of fear. I think far more harm is done by blindly embracing Evolution. I think the heavy push for Evolution is akin to the heavy push to normalize homosexuality, because once it takes root in every day life, then the average citizen is radically corrupted and confused in their thought process.