When talking to people who do not know about polyamory, focus on the things you like about how you live and not
the things you don't like about how they live.
Do not try to justify your ideals by challenging the ideals of others. If that is your only means of substantiating why you believe in something then your viewpoint will come across as negative and confrontational.
Focus on educating, not converting.
Speak in their language; understanding first, vocabulary second