Homophobia has a much longer history than Islamophobia. If a person happens to express disagreement with any aspect of the homosexual political and/or social agenda, that person will be tagged "homophobic." This tag is used to quash criticism and slap a label on people. This label is currently akin to calling someone a racist. It is often applied to Christians, who find homosexuality anathema to God's will. Despite the paranoia and anger homosexuals seem to harbor against Christians, there is no such term as Christophobia -- nor should there be.
Islamophobia is now the new trendy label to throw around. Currently, anyone against building a mosque near Ground Zero is "Islamophobic." Rational arguments against building the mosque are shot down in shame once this term is applied. Again, it's akin to being labelled a racist, which in America seems to be the absolute worst label one may be stuck with. And yet, there is no such mental illness as Islamophobia.
Tossing these labels around is tantamount to covering ones ears and shouting la la la la at the top of ones lungs. It is a cheap, arrogant and pathetic tactic used to win an argument. Most of us, however, see through this petty and immoral maneuver and ultimately lose all respect for the one employing it. It doesn't silence people due to shame; rather, people clam up once they realize they are arguing with a fool.