I believe that there is a difference between 'disagreeing' and 'discriminating'.
To disagree means simply to have or express a different opinion.
To discriminate means to actively take prejudicial action against someone on the basis of a disagreement.
On a personal level, I disagree with the gay lifestyle, just like I disagree with a lot of things that my friends do - and that does include disagreements with their 'identity'. They are still my friends though because we have common grounds through other things.
That being said, I do not discriminate between my friends who are gay and my friends who are straight. I treat them exactly the same - and I would hope this is through kindness and mutual trust.
However, on a broader level - ie. legislating against gay marriage/debates in Parliament - I can see how the line between 'disagreement' and 'discrimination' blurs - hence EZ's earlier argument - as MPs' personal opinions are implemented into laws that affect everyone in the community. MPs are put into the very public situation where their personal opinions against the 'politically correct' view are forced to become discriminatory - because their role is to make laws for the community.
That being said, MPs theoretically should always represent the majority view of their constituency, the majority vote should always be upheld and minority groups should always have the right to express their opinions.
Hope that makes sense.

Again, a reasonable tone and gentleness is likely to come across better than hitting them on the head with a hammer; it's the same thing as teaching.
As has been said previously by EZ, caution and care is needed when expressing views or even trying to present reasons for a particular view as EZ calmly did. In such a topic, I believe it is very easy to become emotionally charged - hence the unfair, prejudicial comments of the MP re 'bestiality'.
Expressing opinions and the reasons for those opinions is definitely important. But it is equally important to respect the views of others.
Obviously, this is really idealistic. Depending upon the person, it mostly works on a personal level. However, such mutual respect probably will never be achieved on a broad level, because unfortunately there is always one party that crosses the line between respectfully disagreeing and blatant prejudice, and hence the inevitable retaliation that follows.