Let’s be specific, as has been addressed numerous times, repeatedly in different threads, they are not talking about the theory of evolution.
They are talking about some
form of the theory of evolution. As far as the simple facts of common descent and biological forms transforming into very different biological forms over many generations - that is acceptable. As Pope John Paul II said in his 1996 address:
And to tell the truth, rather than speaking about the theory of evolution, it is more accurate to speak of the theories of evolution. The use of the plural is required here…
The difficulty with this thread is that there is great reluctance to recognize the variations in the theory and to treat all versions of the theory the same. Therefore we end up with endless arguments that go nowhere. And they will continue to go nowhere until a real effort is made to understand these differences.
One version of the theory states that species turn into other species through many generations. This is the weakest form of the theory because it makes no claim about natural selection or divine intervention or anything. It just states that reproductive descendants can end up being completely different species. This form has not been condemned by the Church. One many challenge it on scientific grounds if one has evidence. All scientific theories are open to being challenged. That is the scientific method. But I don’t believe this weak form of the theory can be challenged on theological grounds - at least not staying totally within the realm of Catholic teaching.
A stronger version of the theory states that natural selection appears to shape the changes that occur as species evolve into other species. This form also has not been condemned by the Church, as long we have a proper understand of what it means for natural selection to “
appear to shape the changes.” This does not mean natural selection
does shape the changes in any philosophical sense. It means natural selection appears to shape the changes if we consider only what can be observed. This is an important philosophical point. The appearance and the “philosophical reality” can be two different things. But science, by its own rules of the scientific method, must be limited to what can be gathered by appearances. Of course this means more than mere first impressions. It means any observation now or in the future that bears on the question.
In a sense, science does not care, nor should it care, what is
real. For all of reality could be a simulation, as in “The Matrix.” But until one manages to go outside the matrix, the science based on what we observe within it is the appropriate science to consider. If evolution is actually directed step-by-step by the mind of God in real time and if He does it in such a way that natural selection appears by every scientific test to be the cause of all the changes, then it is still the right thing to do scientifically to posit that natural selection “appears” to cause evolutionary changes.