I am not. Messianic Jews are Pharisees/modern Jews who believe in the coming of the Messiah (who hasn't come yet) and the resurrection of the dead.
If you are referring to a Christian sect that calls itself "Messianic Jews," you bet I am leaving them out on purpose.
I know several and they would strenously object to being told they are not Jewish Christians. :o)
I am sure they would. However, one thing all Jewish sects agree on is that one cannot be a Christian and remain a Jew, just as one could not become a Muslim and remain a Jew.
Weren't you the one who mentioned the genetic part of Jewishness??? My friends are Jewish by race and Christian in their faith. You are not correct in defining Messianic Jews as modern-day Pharisees who are looking for the Messiah to come one day. They are people who were born Jewish (race and religion) and have converted to Chrisianity from Judaism. They believe that Jesus Christ (Yeshua Hamashiach) is the true Messiah. There are several on FR that post from time to time. Ask them.
As far as a Muslim becoming a Jew or Christian, of course they couldn't because Muslim is a Religion not a race. Can an Arab be Muslim or Jewish or Christian? Yes. See the diff?