Be patient with the world.
Thirty years ago, a MM or FF couple couldn't kiss in public. Even holding hands was considered Too much by some people. The first interracial kiss was on Star Trek in 1967 (I know, I should look it up).
Realize that the average person needs to see things they don't understand. And they will make assumptions. And if it is not their lifestyle, it must be wrong. After they learn more... see the stability in poly relationships, meet the people, read about the challenges, they will accept it.
Give them time... and realize their first reaction... may not be how they finally believe. (you don't want to know my first reaction to poly in real life!)
There are a lot of opinions out there that will change over time... We just need to give them good examples... heck, even bad examples... and in time, there will be changes. (those MM FF couples can now marry in some states, in many countries. We're making progress.)
Be patient with the world... They're confused enough as it is.