When one hears claims about Church history that are less than flattering, or shocking, two balancing perspectives are helpful. 
 
On the one hand, one ought not to become too alarmed or defensive of claims that there has been sin in the Church. Any time there is one human being in the room there is bound to be sin. And The Church is very big and very old. The “hospital” we call the Church includes many saints, but is also a hospital for sinners. 
 
On the other hand, not all claims of sin in the Church are fair, or presented in proper context. And some claims are outright lies, or exaggerations. Thus, it is highly unlikely that 20% of the clientele of prostitutes were clergy. There are, and have been even great sinners among the clergy. But as recent scandals (sadly) show, the percentage of offending clergy is quite small, though even a small number is too many and can cause great harm. 
 
Other claims against the Church regarding the Inquisition in the Crusades also tend to present these issues out of historical context and backload current sensibilities to times that were far more brutal, and where stable governments and modern jurisprudence did not yet exist. 
 
And so, we must have balance. Jesus has always been found among sinners, to the scandalous of some. We do not make light of sin; we simply seek fairness.

Well, Jesus, who was on the scene and rather smart, seems to have concluded differently than the preacher you mention. 
 
That said, we do not usually bring people with seizures to an exorcist, but seek always to rule out natural causes first. In rare cases, what manifests as seizures may have demonic causes, but not usually. So rather than second-guess Jesus, or consign biblical insights to "primitive" thinking, we do better to assess what is before us, humbly realizing that there are often many levels to human struggles. And while some ailments are simply physical in origin, some may include other dimensions as well.