Shidduch Crisis

A definite mamzer may marry a sefek mamzeres but not a kosher Jewish girl. Now, every Jew is only not considered a mamzer because of the דין רוב [most children come from their mother's husband] and the שיטה מקובצת in the first perek of Bava Metzia says that every case of רוב is still considered a safek, just you can follow this רוב.

It emerges then that EVERY Jew is a ספק ממזר. So why can't a mamzer marry anybody??

Is that a KASHYA????

HELP!