As we published in our article on Don Bosco, the saint wrote the following in his periodical entitled Catholic Readings:
My dear friends, the enemies of Catholicism, and especially the Waldensians, are doing their utmost to undermine our beliefs. We exhort and urge all who cherish the Faith of their fathers to join us in defending this most precious gift of God. Help us to spread Catholic Readings so that we may un­mask deceit and heresy and safeguard the Catholic Faith of our people. It alone has the whole truth. Without it one can­not please God. Outside of it no one can be saved.
Don Bosco
In another issue he wrote:
The Catholic Church is the only Church founded by Jesus Christ. No one can call himself a Catholic and still reject the Pope. Disaster awaits one who cuts himself off from the Vicar of Christ; he will become an outcast without salvation. One who does not have the Church for his mother cannot have God for his father.
Let the same Faith, the same commandments, the same sac­raments, and the same charity unite us all in life and in death. Above all, let us take advantage of the sacrament of Penance, the powerful means instituted by Christ Himself to confer the merits of His passion and death on our souls, to free them from the clutches of the devil, and to shut the gates of hell while opening those of heaven. Amen.
In 1979, when Brother Francis memorialized the recently-deceased Brother Hugh, he mentioned Brother Hugh’s role in the conversion of a prominent Italian-American Waldensian,
…Professor Augusto Bersani, a leader of the Waldensians [also called the Waldenses]. Brother Hugh labored “with the patience of Job” for twenty-five long years before achieving the conversion of this brilliant man who somehow had wandered into the poisoned pastures of heresy. Professor Bersani finally sent for a priest on his deathbed, and made his peace with God.
Like Don Bosco, Brother Hugh had insisted, over and over again, that the Waldensians cannot be saved as Waldensians, but only as Catholics — which, of course, requires conversion. Professor Bersani argued a lot, but was eventually won over. When we tell them they can be saved in their false religions, this sin against charity does not help them.
It’s like telling an alcoholic that it’s OK to indulge his appetite for booze, or an obese man that twelve Big Macs are healthy fare.

http://catholicism.org/don-bosco-eens-and-the-waldensians.html