The existence of the sects or cults of Christianity that deny the deity of Christ is not a “Protestant” problem. Arianism was around long before the Protestant Reformation.
Also doctrinal differences, go to an Anglican church and you’ll hear “Mary Mother of God” go to an evangelical church and you’ll hear nothing at best and you’re quite likely to get some rant about how Mary in Marian apparitions is actually a daemon.
These are big differences and I don’t see how the Holy Spirit can play a part in there existence.
I agree. There are two passages of scripture that Evangelicals (I don’t know about Catholics) mainly go to in order to justify their presupposition that the Holy Spirit can illumine our minds to understand and know everything that is in the Bible:
(1) 1 Corinthians 2:10-13. However, in context the apostle is referring to the “message of the cross” that is being rejected (1:18) and the crucifying of the Lord of glory (2:8). Thus “what we speak” (the “spiritual truths”) concerns the gospel. God has given us his Spirit to understand everything we need to know about the gospel - not about every point of doctrine or theology.
(2) 1 John 2:27 refers to the anointing of the Spirit which will teach us about “all things”. Again, in context, this anointing refers to knowing the truth that Jesus is the Christ, the Son of the Father (vv. 20-23) – it does not concern every point of Christian doctrine.
What I’ve written may be scary to the reader who would like to have an apostle or leader over us to teach us the “truth” about every point of Christian doctrine. But as soon as this happens, Christian unity and fellowship is broken and divided as we claim to have all the truth, and nothing but the truth.