I'm probably the complete opposite of most people here, I presume. I can easily find a lot of bad sides to zoophilia but I struggle to find a single good one.
I think my biggest issue with it stems from how society perceives the emotional and physical aspects of zoophilia. Simply expressing a desire to form a romantic relationship with an animal is at best ridiculed and at worst met with hostility. It's not something that is taken seriously, encouraged or condoned in any way. And as we all know actual sexual acts with animals are seen as completely unaceptable. This of course means that expressing such a sexuality is illegal in most places, but it also pervades through society in more subtle ways. People won't help a zoophile achieve his or her dreams or ambitions. They won't take them seriously or try to understand them. Zoophilia is seen as a sickness that has to be treated, never as a legitimate pursuit.
Because of this, zoophiles live in fear and secrecy. They often can't connect to other people. Even if the rest of society doesn't care to help them, they often can't even help each other due to the severe repercussions that can follow being exposed as one.
Another issue with society is that animal life is considered much less important than human life. This can manifest itself in several ways that could be harmful to zoophiles and their family.
Next up, there is the issue that animals have much shorter lifespans than humans. Most species of animals simply can't be life partners to a human due to their short lives.
In my own personal life, I have struggled a lot with the sexual side of things. Being exclusively zoo means I have no other outlet for my sexuality and I have never managed to find that connection with an animal. No matter what people who have never gone through something like this can say or think, people in a similar situation tend to agree that prolonged celibacy can rot your mind. I am now suffering from severe depression due to pursuing that dream in vain for decades.