We protestants recognize that there are many Christian Catholics, but this is in spite of their church rather than because of it. The RCC has added so many non-Christian and even anti-Christian elements to their religion that it is barely recognizable as Christian.
They pray to (i.e., worship) saints, especially Mary. They burn offerings (i.e. candles) before graven images (i.e., saints) in most of their churches. These are essentially pagan elements that they have overlain Christianity with.
But these are not the worst problems with the RCC. They also teach that Jesus' work on the cross is not enough to completely save. This is utter blasphemy. The RCC, to line its pockets, invented Purgatory. This is anti-Christian.