If “infallible” means “not liable to deceive”, it is infallible - by itself, BTW. Whether it is inerrant, is another matter. The Magisterium is not its master, but its servant, & must heed it, as it contains the whole counsel of God. Which is not to say that it contains enough for our curiosity - nothing does; but it does contain enough for our salvation.
As it is the Word of God, it is irresistible in carrying out the whole of His Will. So its misuse is sinful, but in no way destructive of it; no more than a whirlwind is destroyed by having a stick shaken at it. What makes it effective is not the Magisterium but the Holy Spirit: without the Spirit of Christ, it is lifeless & dead, like the Magisterium, the Church, & all that is therein.
