What were they thinking?

Did they assume those savages will work for them forever and that it will never have any impact on the demographic state of the country?

Nevermind the crime (unless their violent nature was not known at that time, which I doubt).

Also, is anyone surprised by how much the Portuguese overtake the Brits in numbers of slaves traded?
Even Spain had bigger numbers.

Source:
https://en.wikipedia.org/wiki/Atlantic_slave_trade#Destinations_and_flags_of_carriers