Why are Catholics so afraid of those?
I wouldn't say we're afraid... disgusted or saddened maybe. Because those are errors. I could ask why you're so afraid of Purgatory, Confession, the Assumption, the Immaculate Conception, etc. and presumably you'd say something along the lines of those being false teachings. Well that street runs both ways.
It has to be fear. Sola Scriptura - relying on what Christ and the apostles taught without adding anything.
Sola Fide - Putting all of our faith and trust in Jesus alone. Paul taught that it gives righteousness, justifies, and sanctifies. It results in the indwelling of the Holy Spirit guaranteeing our salvation.
once-saved-always-saved - Jesus said that those who God calls to be His will never be lost.
The only reason to fight against that is that Catholics fear that what the Catholic Church has added may not be true if scripture alone is true.
>>I could ask why you're so afraid of Purgatory, Confession, the Assumption, the Immaculate Conception, etc.<<
I don't fear them. They were not taught by Christ and the apostles. Paul said anyone who teaches something they didn't was to be considered accursed. I'm not going to take the risk that some men "got it right". I'll rely confidently on what Jesus and the men He chose said and taught. I would submit that Catholics fear that if that is true and then they are relying on something they cannot verify from infallible sources.