I've mostly heard that characterization from men who are sure that poly women are out there sharing all the most "desirable" men and their husbands are sitting home alone, crying in their beer. They don't like to hear that overwhelmingly, this isn't the case. I explain to them when you don't have to have only one person be your everything, more people are likely to find partners. That blows their mind, right there.

Glad your friend finally stopped looking at you as competition. That's a counterproductive mindset for anyone because you're right - nobody can "steal" your partner.