Basically, the Cathars were are sort of dualists, also known as the Albigenisians. They believed that material, created by Satan, was evil whereas the soul was divine. They were a movement from which the Inquisition originated.
From a primary source, an inquisitor who assessed the Cathars' disbelief in the efficacy of such sacraments because they involved material - and therefore evil - substances:
Then they attack and vituperate, in turn, all the sacraments of the Church, especially the sacrament of the eucharist, saying that it cannot contain the body of Christ, for had this been as great as the largest mountain Christians would have entirely consumed it before this. They assert that the host comes from straw, that it passes through the tails of horses, to wit, when the flour is cleaned by a sieve (of horse hair); that, moreover, it passes through the body and comes to a vile end, which, they say, could not happen if God were in it.
Of baptism, they assert that the water is material and corruptible and is therefore the creation of the evil power, and cannot sanctify the soul, but that the churchmen sell this water out of avarice, just as they sell earth for the burial of the dead, and oil to the sick when they anoint them, and as: they sell the confession of sins as made to the priests.
Hence they claim that confession made to the priests of, the Roman Church is useless, and that, since the priests may be sinners, they cannot loose nor bind, and, being unclean in themselves, cannot make others clean. They assert, moreover, that the cross of Christ should not be adored or venerated, because, as they urge, no one would venerate or adore the gallows upon which a father, relative, or friend had been hung. They urge, further, that they who adore the cross ought, for similar reasons, to worship all thorns and lances, because as Christ's body was on the cross during the passion, so was the crown of thorns on his head and the soldier's lance in his side, They proclaim many other scandalous things in regard to the sacraments.