Well, I'm not naive, and I'm no FFB either. The vast, vast majority of Jews don't eat Kosher food. And most of those who don't eat Kosher food aren't sinning out of a rebelious contrariness. Most of them are rather ignorant or unaware of what Kosher food really means. That was my situation until during my teens I got involved with NCSY.
For many Jews, the "traditional" seder they know from their childhoods was not kosher. The fish may have been "geffilte," and not shrimp, but the plates were most probably the same ones set out for any festive meal during the year. So if they go to the "Jewish Seder" in some traif restaurant, it's no less kosher than what they would serve at home. Maybe they'll read through the Haggadah a bit to get familiar with the story. And maybe it will set a Jew on the way to a truly Jewish life, G-d willing.