I am sorry that you have been hurt and offended by the answer that you read. Unfortunately this question/answer forum does not lend itself easily to giving fullsome and well developed answers. However let me try to answer some of your concerns.
The question of the Catholic / Protestant churches is a long and difficult one. It goes back to the time of the Reformation when a handful of people sought to reform a corrupt Catholic Church. The Church had become corrupt because it had misinterpreted and mishandled the bible to the extent that Christinity had become a religion of works rather than faith. Catholics were encoraged to buy indulgences to help loved ones who had died, escape the penalty of Purgatory. The Protestant Churches that arose out of the Reformation sought to correct this by teaching the authoirty of the Bible above all other things including the Church and that salvation come by faith alone and not works.
Since then much has happened on both sides of the camp. Some parts of the catholic Church have become quite Protestant in their thinking and some parts of the Protestant Churches have become quite Catholic. It has got to a point where there is so much variety in belief on both sides that it is hard to make generalisations about either. There is teaching in some parts of the Catholic Church that I think are unbiblical just as there are teachings in some the Protestant Churches that are unbiblical. It has got to the point that for every example of error I can find in one church I can find the same in the other. And for every true Biblical teaching in one church I can find the same in the other.
The person who wrote the answer that you read has made just such a generalistion. Yet I know of Catholics who believe and teach the things he was writing against just as I know Catholics who would be just as offended as you are. The issue is not that they are Catholic but what they believe the bible says about salvation. And this was the point that the person who wrote the answer was trying to make.
However given this (and given that I am not an expert in catholicism), there are some official doctrines of the Catholic Church which are hard to justify biblically such as the status of Mary in the Church and salvation. Such doctrines can lead people away from the truth, away from putting their turst in Jesus and him alone. And to this extent they are dangerous and to be avoided. This was the point the person who wrote the answer was trying to make.
While ever a person’s faith is in Jesus and him alone then they are my brother/sister but if they are trusting in more than Jesus then they are denying him entirely and they cannot be a Christian. This goes whether they are Catholic or Protestant.
Now I hope I have not offended you again. I have tried to treat this difficult topic fairly.