The idea of sinless perfection is the most indefensible of any religious concept. Indeed, if there is one thing that unites all men, of all religions, save for Christ alone, it's hypocrisy. No matter what your religion is, the fact that you are not God means you will not always live consistently with it. No Muslim is a perfect Muslim. No Hindu is a perfect Hindu. No Jew is a perfect Jew. No Christian is a perfect Christian.
It is worth noting that aside from its explicit statements (e.g. 1 John 1:8-10), Scripture is also written with the assumption that sinless perfection is a gift from God that will only be opened when our life ends. James, for example, tells us that we should not all become teachers, as these will be judged more strictly. Yet we all offend in many ways.
James continues to say that if anyone controls his tongue, he is perfect, which of course fits in nicely with Jesus' prior statements that it is not what goes into a man that defiles him, but what comes out (see Matthew 7:1-23). The things that "come out" of us (by our words and deeds) are the horrible things that live in us. Greed, theft, murder, sexual immorality... pride. When James says we're perfect if we control our tongue, it's not because the tongue is some kind of free willed entity separate from ourselves, forcing us to sin. It's because as we are in our hearts, so are we in our speech. If you're sexually immoral, you will speak sexual immorality. If you're full of hate, you will speak of murder. If you're greedy, you will speak selfishness. If you're full of pride, you will speak of sinless perfection, because whereas James says we shouldn't all become teachers because we all offend in one way or another, you say you do not offend in some way or another, and so your tongue speaks pride.
From the beginning of history until today, only one man has achieved sinless perfection. He died on a cross because you haven't. Let us not speak pride or folly, but rather let us speak repentance and gratitude, for though we are far from public, our great God took on our sin so that we may become His righteousness.