For one thing, I don’t think the interview board will ask you controversial issues which might make both you and them uncomfortable.
There are two ways in which you can still approach the question if it is asked and it depends on what kind of person you are.
If you are the practical type, who believes that what you say in the interview is not a reflection of the stand that you are going to take in all time to come, you can simply go by the government and the constitution and support the reservation system. And there are very good arguments that actually can be put forth in favour of the reservation system.
If you are an idealist and believe that you would only stand by what you believe in, then go ahead and tell them that you think that the reservation system is flawed. The interview board never minds a differing opinion. They in fact encourage non-conformist opinions, which are well backed by good arguments. However, don’t play debate there, and be humble while expressing your opinion.
It is not whether you differ that matters, but how you differ that does. Be careful while treading that line.