Angainor:
Catholics commonly say to Protestants, “with all the denominations out there, each interpreting the scripture their own way, how do you know which is right?” The bible gives us a way to know:By their fruit you will recognize them. Do people pick grapes from thornbushes, or figs from thistles? Likewise every good tree bears good fruit, but a bad tree bears bad fruit. Matthew 7:16-17
I wonder how Catholicism’s fruit should be judged. Europe comes to mind. It has a long history of Catholicism.
Just about anywhere except those countries - the USA, Australia, New Zealand, parts of Asia or Africa - where Christianity of rather recent growth, would be worth a look.
What is very unconvincing, is the suggestion that it has not been tried. This defences raises two difficulties, perhaps three:
- The pre-medieval cultures of Rome & Byzantium thought they were trying it: were they pagans all along, without realising it ? Granted, they did some foul things - but how is this to be interpreted ? A Christian Emperor who has the sons of his predecessor castrated in order to stop them having sons who might challenge him in the future, is not being very Christ-like; neither is a bishop who has his enemies blinded, as St. Martin III did - but they thought that they were Christians; their contemporaries thought so - and we too do foul things: does this mean we are not Christians ?
There is also the ethical problem - past generations had no qualms about ripping French regicides apart with wild horses, burning heretics, disembowelling English traitors, breaking people on the wheel, or torturing rebels to death. These activities would now be regarded as morally problematic. So, is a ruler who rips out the tongues of blasphemers, boils poisoners alive, and saws the heads off rebels, acting as the Christian he thinks he is, or as a monster of cruelty ? By the standards of his time, boiling poisoners may seem wholly consistent with the Gospel - today, it would probably not. So who is the Christian here ? - that, is the problem.
There is a subsidiary problem: many of those regarded as saints have done things which no Christian would dream of doing now - what does this say about what Christians regarded as holy actions ? Part of the answer, perhaps, lies in the diversity of ways in which Christians have pictured Christ & God: there has been Christ the Man of Sorrows, the Victor, the King, the Priest, the Wounded Healer, the Eucharistic Victim, & many more. If Christ hates heretics - then burning them alive is no big deal. 17th century writers - de Montfort, for instance - seem to imagine Heaven as a sort of Versailles, with Jesus being, like the Dauphin or like Louis XIV, far too exalted for us ordinary folk to approach. More recently, there has been Christ the Worker.
What does seem clear, is that no age is more finally right in all respects than another.
According as Christ is pictured, so do His followers act.
- If Christians who do cruel things are not trying to be Christians (in the eyes of their later critics) - where is the Church ? The trouble with us, is that we are all sinners: and if being sinful is to stop us being Christian, then the Church ceases to be a visible body; one is left with a “hyper-Donatist” ecclesiology, in which one ceases to be Christian the moment one ceases to be perfectly holy. OTO, if one can be a sinner and a Christian - what sins, if any (& why?) - are incompatible with being Christian ? If it is not a contradiction to speak of a Christian soldier, or of a Christian executioner - why is it a contradiction to speak of a Christian usurer or adulterer or thief or prostitute ?
ISTM that your question raises a lot of issues: about ethics, reason, ecclesiology, Christian self-understanding

Do you have the answers ?
And what notions of God do the answers people give to these questions presuppose ?
As for the good qualities of the Church - any church: they would count for something
if the Church’s constancy in this matter were of her own making. It’s not; for if the Church has good qualities at all, they come to her solely from Christ. She can never boast of any good in her, simply because the good, in her, is not from her in the first place. ##