To understand how and why some Catholics have an unsavory reaction to Protestantism, you have to look at the history behind it. In the USA it was Illegal to be Catholic in all of the Original Colonies except Maryland. When Protestants gained a majority in Maryland, Catholicism became illegal. In Protestant countries many Catholics where killed for practicing their faith. The torture and martyrdom of Catholics was far more brutal in England, Scotland and Ireland (Then under British Rule) than in any Catholic country. When Irish and Italian Catholics came into this country there where discriminated against in jobs, and there where a number of Anti-Catholic groups that went so far as to burn down Catholic Churches. Still today in Northern Ireland Catholics cannot own property, and therefore cannot vote. Catholics are banned from various professions and schools in Northern Ireland. There are many grudges on Both sides that are due more to non-doctinal issues in the past than religious belief.

The simple answer to your second question is that they are Christians who are not in perfect unity with the Church.

To paraphrase what Pope Pius XII wrote in his encyclical “The Mystical Body of Christ” There is one baptism, it makes someone a Catholic, and if seconds after they are baptized they fall into error by accepting the teachings of Martin Luther, John Calvin, John Westley or any other man who founded a Protestant Church they are separated from full communion.

Vatican II also spoke of the imperfect unity that Orthodox and Protestants have with the Church.

Jesus only founded one Church, with one Truth. In the Bible we read that He promised to remain with the Church even to the end of time. The Church from the very first days has because it is composed of humans, had need of reform. Each of us daily has to reform our lives to become closer to Jesus our Master. As Catholics we need to admit our shortcomings, and stive to “be ye perfect, as My Father in heaven is perfect.” and set an example of what Christ has called us all to be.