I think you misunderstand the Catholic Marian teaching of the Immaculate Conception. It has nothing to do with the virgin birth of Jesus Christ, but rather the dogma that Mary was born herself without sin.
To address your question: Jesus Christ is is worshipped as part of the holy Trinity because he was God incarnate, died on a cross for the sins of the world and was resurrected from the dead and lives today. Obviously there are many people who think this is not true, but you asked a question and this is the reason that, I believe, Christians revere and indeed love Jesus.