Birth control, abortion, the pope.

... praying to saints (and the whole creation of saints to begin with), hail marys, penance, pergatory.

Huh, I keyed in 'pope' to the search function and the word wasn't mentioned in the article.

I'm gonna go with 'the pope.'

Lock in 'The Pope', Eddie.

As another poster said, abortion's another one - more specifically, contraceptives.

It is fascinating to read Peter Sellick’s enthusiasm, for closer affinity with the Bishop of Rome by Christians beyond his control, and compare it with Catholic Paul Collins’ numerous writings against that dictatorship (but not against his church).
Billie has summed up the basics impeccably.

Peter, I think you are getting some pretty fundamental philosophical relationships wrong here. Protestantism begets individualism, rather than the other way around, and the individualism of protestantism comes directly from the gospels, and Socratic philosophy as transmitted by Paul and Augustine. Catholicism is the hold-out of Aristotelianism.

The reason why protestants like me would never become part of the Roman church is because it is prescriptive and collectivist. While the practice of many Catholics may be in principle quite protestant, as might be the outpouring of some Catholic theologians, that is because we in the west live in a Protestant world, Luther et al having won the battle of ideas.

And it is a much better world for that.

Whilst I am not terribly fond of saying such things, but Peter Sellick's writings are becoming increasingly indistinguishable from those of a soggy cardboard box.

Apart from the previously mentioned issues, one could also suggest congregational control ("Priesthood of all believers", Hussites), and the Catholic positions on prima scriptura and sola fide.

These are generally considered absolutely core points of differentiation between Catholicism and mainline Protestantism. Then there's those of the Radical Reformation, such as the rejection of childhood baptism, and those who rejected Nicene Christology, such as the Socinians and various forms of Unitarianism.

All of this is very basic to understanding the difference between Catholic and Protestant thought and the fact that Peter Sellick doesn't even mention the issues indicates his extraordinary intellectual poverty when it comes to writing on religious matters.