People who have taken Christianity only by name and have used the name wrongly. The Catholics are no doubt who you are referring to.
Given that what you say has happened it leaves the question; should it have happened given that as you say Christianity is the true religion or faith?
Try to follow along and think about it because this answer does make sense:
Jesus gave an illustration showing that a corruption would happen to Christianity. Note the following scriptures:
(Matthew 13:24-30) . . .Another illustration he set before them, saying: “The kingdom of the heavens has become like a man that sowed fine seed in his field. 25 While men were sleeping, his enemy came and oversowed weeds in among the wheat, and left. 26 When the blade sprouted and produced fruit, then the weeds appeared also. 27 So the slaves of the householder came up and said to him, ‘Master, did you not sow fine seed in your field? How, then, does it come to have weeds?’ 28 He said to them, ‘An enemy, a man, did this.’ They said to him, ‘Do you want us, then, to go out and collect them?’ 29 He said, ‘No; that by no chance, while collecting the weeds, YOU uproot the wheat with them. 30 Let both grow together until the harvest; and in the harvest season I will tell the reapers, First collect the weeds and bind them in bundles to burn them up, then go to gathering the wheat into my storehouse.’”
(Matthew 13:36-43) . . .Then after dismissing the crowds he went into the house. And his disciples came to him and said: “Explain to us the illustration of the weeds in the field.” 37 In response he said: “The sower of the fine seed is the Son of man; 38 the field is the world; as for the fine seed, these are the sons of the kingdom; but the weeds are the sons of the wicked one, 39 and the enemy that sowed them is the Devil. The harvest is a conclusion of a system of things, and the reapers are angels. 40 Therefore, just as the weeds are collected and burned with fire, so it will be in the conclusion of the system of things. 41 The Son of man will send forth his angels, and they will collect out from his kingdom all things that cause stumbling and persons who are doing lawlessness, 42 and they will pitch them into the fiery furnace. There is where [their] weeping and the gnashing of [their] teeth will be. 43 At that time the righteous ones will shine as brightly as the sun in the kingdom of their Father. Let him that has ears listen.
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So if you can understand this is a prophesy from Jesus time up until the harvest or Jesus return. Jesus referred to it as what he had started ("Christianity" or the fine seed) would be like a field of wheat. When this field started and was just planted, it had only just started to grow and everything was good. Then in the meantime an Enemy (Satan) over sewed the field with weeds, hence corrupted what was good with bad. In the illustration the workers returned and informed the master what had happened and what to do. The master (Jesus) said to let them grow together until the harvest.
So Jesus was saying that Christianity would be corrupted by the figurative weeds. But he wanted to let them grow together until the end and this was to fully display itself above the weeds so that at the conclusion or harvest, it would be well above the weeds and figuratively easily harvested.
So the weeds or corruption would still be existing at the end. What would happen to them? They would be gathered and burned.
Something most people do not understand is God wants us to work to know him and select based on our efforts. It is obvious who the wheat are and who are the weeds. There is one true Christian organization and many false.
Satan although he is the enemy of God has it in his purpose to make it hard to get to know God. Satan roots out all who are not strong and perceptive to God's ways. It is a sad thing, but a lot of people will miss out due to ignorance because God in these last days, makes things fully displayed for all to make the correct decision. It is up to each individual to choose wisely.