no problem at all, if everyone agreed all the time, the hobby wouldn't advance. The vast majority of us aren't marine biologists so we are just going with experience and second or third hand information.
If I remember correctly I read it in a more reputable place than another forum online, but it was some time ago.
If the coraline algae blocking the pores from the water column, it would cause small amounts of water to become anoxic (no oxygen) as opposed to anaerobic (low oxygen). But like you said, the coraline is porous as well, I just don't know if it is porous to the extent that live rock is to cause the anaerobic conditions. There is also the issue that the coraline is continuously over growing itself.
As far as the natural process of things, Rocks on the reef don't get coraline growth like many people see in their tanks. I see a lot of aquariums that are very purple, and I don't remember ever seeing natural reefs that are dominated with so much purple. It's growth in the wild is usually spotty from what I have seen. Also, as far as I am aware, most of the filtering of sea water is done by non-coraline deep water algae.