To begin with, formally speaking the Spanish Inqusition only had jurisdiction on cases involving the Catholic religion. So they did not have authority over non-Catholics unless it has to do with apostasy. The voluntary and forced conversions following the fall of Granada (see Ximenes' policy on forced conversion) created new classes of Conversos and Moriscos, respectively Jews and Muslims who converted.

Further, there was never a single monolithic Catholic opinion, not then and not ever. So you have to accept that at best you'll get a survey as an answer, and the space of reddit is insufficient to fully answer what you are asking for, even if it is what you are asking for. The situation varied widely between locales and different groups of people. And truthfully, quantitative research into the Inquisition is still ongoing and a lot is still unknown.

The Spanish Inquisition was popular at times and places where there were genuine fears of a Converso plot against Christians. They were popular as there were growing fears of Morisco plots, in collaboration with Ottoman agents, against Christians. Otherwise, broadly speaking, they were not popular, even if they were often used as a means to hurt one's adversaries and competitors. This was a very common theme as forced conversion conferred a benefit to those who followed through: they were given access to jobs and positions they did not have access to when they were not Christians. Naturally, this generated conflict against the old Christians.

The first period of the Spanish Inqusition saw the office focus primarily on Conversos. Many had been financiers to the crown prior to their conversion; following conversion, they could then be appointed to public office. This led many old Christians to complain that the conversion had been insincere, that they were secretly practicing Judaism and pretending to be Christian. The Conversos deflected this accusation towards Jews, who they accuse of proselytizing. Aspects of this played into the expulsion of Jews from Spain.

The second period saw the office investigate many Moriscos, who not only dressed and lived differently and quite apart from Christians, but also was accused of supporting Ottoman agents in the Mediterranean.

Finally, the most important aspects of the Spanish Inquisition are:

• That it is formally controlled by the crown, and to quote Ferdinand II of Aragon, "The hermandad would soon be joined with an Inquisition and, together, employed as an instrument of terror and obedience."

• That as an inquisitive body, there were rules and regulations on inquiry, investigation (including strict rules on the use of torture), punishment.