It is really important to remember when an interviewer asks, what is your opinion, this is not the time to try and re-write the law or to argue a strong case. State your thoughts as the question suggests, but remember to be respectful of the law. No employer wants to hire a candidate who may be willing to go against a policy, simply because they don't agree with it.
"This is a question that often causes some conflict among those of us in veterinary medicine. Regardless of my opinion, if the law where I am practicing mandates spaying or neutering, I will advise pet owners who bring their pets to me of the law and offer my services."
"I'm actually in favor of mandatory neutering and spaying laws. I understand that others may disagree with me, but I have done volunteer work in shelters and animal rescues and have seen the conditions that many unwanted animals are left in."
"I have to say that I am a bit 'on the fence' with regard to mandatory spaying or neutering. I understand the rationale behind the law, being that there are so many overpopulated shelters and rescues and that some people run what is commonly referred to as 'puppy mills.' On the other hand, having owned several animals myself, I understand pet owners wanting to have a new litter, especially when a pet gets older and nears the end of life. Having said all of that, I am obligated to abide by the law and by the policies at the facility where I work and will do so."