There are plenty of us who were poly when entering our current relationships. My wife was involved with a couple prior to meeting me. I'd had some mono an some open relationships prior to meeting her.
I don't think there's any guaranteed way to avoid the "poly repulsion" reaction. I just view it as part of the regular screening process. If a person can't even consider being involved in a poly tangle--while only having one partner in it and thus staying monogamous--then that person really isn't compatible at all and not worth considering further.
I have no problems with folks who only want a single relationship to deal with themselves and think they could have a place in a poly tangle. It's when they expect a partner to also only have a single relationship that they remove themselves from poly-compatible. I don't consider anybody who's not poly-compatible or outright poly to be a potential partner, much the same as I don't consider lesbians to be potential partners. They might be wonderful, attractive people--they just aren't for me and I don't lose sleep over it.
Although my first wife played D&D all those years ago, I can't say that I've ever met a single dating partner via gaming. Even freelancing in the industry never landed me a date.
When speaking of various forms of non-monogamy...it ain't poly if you're just fucking around.
While polyamory, open relationships, and swinging are all distinctly different approaches to non-monogamy, they are not mutually exlusive. Folks can, and some do, engage in more than one of them at a time--and it's all good.