Check out http://learningteshuvot.blogspot.com/2011/04/inviting-non-jews-to-seder-bmareh.html There is no prohibition for inviting Gentiles to a Seder table. Special consideration must be given to food preparation in view of expected gentile participation, that is all. Also, there is no such reference to the sin being there in the Torah. In fact, Torah is very clear as to the treatment of non-Jews in its midst and that is NO DIFFERENCE between Jews and non-Jews in anything other than religious services.
Israeli troops shoot, injure Palestinian crossing Gaza border fence (Haaretz)
from the article: Matzah balls at the White House: Obama hosts third Passover seder