Religion during the GAoP

[Fox]

The other thing to bear in mind is that belief and practising religion are not always the same thing. Pirates who all expected to go to Hell together may not have practised religion, but they believed in Hell (and thus, presumably, the alternative). Other pirates are known to have practised religion, such as Taylor's company who sang psalms at the funerals of their comrades, and even went so far as to ban the discussion of religion in their articles - presumably because of its potentially divisive nature - but du Bucquoy says that apart from funerals he never saw them doing anything else religious.

[Guest]

This system had been introduced with heretical English or Dutch pirates in mind

I think the part you are missing here is Heretical The Dutch and English Pyrates would have been Protestant, and therefore considered heretics by the Catholic Spanish.

If I remember correctly, if English Buccaneers were captured by the Spanish, they were tried first as Heretics, and if they "survived" that, then they were tried for their acts of Pyracy.