Okay, I'm going to represent the other side of things for a second...

My now-wife had a bunch of cats when I met her. I don't hate cats, but I don't want my house smelling like cat poo, and I certainly do not want any other things that might ride in on the cat.

Long story short, I let her bring the cats. They reproduced, made more cats, and it smelled like poo all the time. Things got scratched, marked, etc. as well. We moved into a place that doesn't allow cats anyhow, so she ended up getting rid of them. Later on the landlord caved and after a year of begging she got another #$%$%#$ cat. Six months in the cat ran away, but not before smelling up the place and bringing in fleas, which I'm still fighting with even as I type.

So if you can address the major concerns he has (mine would've been 'I promise to change the litter every day' and 'the beast will never leave the house, so no fleas'). He might be more willing to work with you if you let him know up front what's involved.

Also, my wife hated snakes when I talked her into getting Milton. Now she is crazy about him!