Good point, but some are actually ignorant, i.e. the non-medical help.
Regardless, I believe that this is akin to expelling demons from a home.
From the old Catholic Encyclopedia:
Other exorcismsAccording to Catholic belief demons or fallen angels retain their natural power, as intelligent beings, of acting on the material universe, and using material objects and directing material forces for their own wicked ends; and this power, which is in itself limited, and is subject, of course, to the control of Divine providence, is believed to have been allowed a wider scope for its activity in the consequence of the sin of mankind.
Hence places and things as well as persons are naturally liable to diabolical infestation, within limits permitted by God, and exorcism in regard to them is nothing more that a prayer to God, in the name of His Church, to restrain this diabolical power supernaturally, and a profession of faith in His willingness to do so on behalf of His servants on earth.
The chief things formally exorcised in blessing are water, salt, oil, and these in turn are used in personal exorcisms, and in blessing or consecrating places (e.g. churches) and objects (e.g. altars, sacred vessels, church bells) connected with public worship, or intended for private devotion. Holy water, the sacramental with which the ordinary faithful are most familiar, is a mixture of exorcised water and exorcised salt; and in the prayer of blessing, God is besought to endow these material elements with a supernatural power of protecting those who use them with faith against all the attacks of the devil. This kind of indirect exorcism by means of exorcised objects is an extension of the original idea; but it introduces no new principle, and it has been used in the Church from the earliest ages.
Yes, that is why I am in favor of the exorcism. There is always the chance it will expel a demon from an individual who was involved somehow but not in the spotlight and maybe not fully cognizant. Or a devil hiding in the corner somewhere akin to the home.