I actually more or less agree with you. However, I think that "porn" is a rather broad category, and I also think trying to reduce it to a binary argument of "porn should be allowed" versus "porn should not be allowed" oversimplifies the issue.
MLP-related porn, and the broader category of hand-drawn (or 3D animated) R34 type stuff based on fictional properties, I think falls into the category of fairly innocuous porn that causes little to no social harm. It's mostly niche pornography that appeals specifically to fans of the franchise, and has little appeal outside of the niche. You can also dismiss a fair amount of it as parody or humor although let's be honest here, we all know that most of us unironically wank to this stuff
Anthro porn and humanized loli porn and things like that are considerably more disgusting, but it still falls within the category of niche appeal. "Commissions" are usually requested by a very small group of dedicated fans, and drawn by an even smaller dedicated group that churns this stuff out. A larger but still comparatively small group of orbiters lurk around communities like e621 and paheal to collect and categorize it. These are basically people who elevate hobby-related porn into a hobby of its own. I'm guessing most of us can probably say that we have a horsepussy folder somewhere on our hard drive, but also that our lives don't revolve around collecting, creating or consuming it as is the case for some.
You can probably compare niche pornography fandoms (furries, cloppers, people obsessed with weird fetishes like vore, etc) to habits like meth consumption or drinking moonshine. The people who draw this stuff are basically the guys who operate barnyard stills or basement meth labs, in that these are usually not large-scale mass-distribution operations, but small-time businesses created by people who are participants/addicts themselves, who sell mostly to a small number of dedicated clients. Is it healthy to be involved in something like this to the point that it consumes a major portion of your life? No, and there is arguably broader social harm if people's obsessions/addictions cause them to start doing antisocial things, for instance a lolicon addict who suddenly decides he needs the real thing and starts kidnapping children. However, I think that Post too long. Click here to view the full text.