In Joseph Conrad's Heart of Darkness, the pilgrims are not missionaries. They are called pilgrims, it seems, because they carry long staves or poles. They are agents, employed at the Central Station, and their only desire is to get a job at a trading station: they do nothing, they only want ivory to make money, they hate each other, and treat the natives badly.

[The pilgrims] beguiled the time by back-biting and intriguing against each other...There was an air of plotting about that station...The only real feeling was a desire to get appointed to a trading-post where ivory was to be had, so that they could earn percentages. They intrigued and slandered and hated each other only on that account-- but as to effectually lifting a little finger--oh, no. 

The pilgrims travel with Marlowe to the Inner Station to find Kurtz and bring him home. As abiding as the dust, little changes with them:

The pilgrims could be seen in knots gesticulating, discussing. Several had still their staves in their hands. I verily believe they took these sticks to bed with them.

At the Lower Station, Marlowe had witnessed the pointless blasting of a cliff that did not stand in the way of the men working. Machinery was left to rust indiscriminately across the land. Waste was at the center of the Company's efforts in the Congo...except for people like Kurtz who shipped out enormous amounts of ivory. The pilgrims, also, waste resources and time:

There was an old hippo that had the bad habit of getting out on the bank and roaming at night over the station grounds. The pilgrims used to turn out in a body and empty every rifle they could lay hands on at him...All this energy was wasted...

As the ship travels through the water, the men on the boat hear screaming. There seems to be a great sorrow among the natives to see the steamboat moving farther inland. But these white men, these pilgrims who "work" for the Company, have no regard for the indigenous (native) people: their guns speak for them:

The pilgrims had opened with their Winchesters, and were simply squirting lead into that bush. 

This lack of regard for the native people of the Congo came straight from Leopold II of Belgium who established a Belgian colony in the Congo:

Leopold II described his motives to the rest of Europe as springing from a desire to end slavery in the Congo and civilize the natives, but his actual desires were for material gain. 

The whites that worked for the Company were also fed simply by greed (including the pilgrims Marlowe speaks of in the novel).

The bloodiest single episode in Africa's colonization took place in the center of the continent in the large territory, known as the Congo. 

Leopold's invasion included 19,000 men with repeating rifles, taking on natives with spears and a few old muskets. The black natives were enslaved and casually murdered. Women were raped.

However, there were missionaries in the Congo:

To curry diplomatic favor, [Leopold] allowed several hundred Protestant missionaries into the Congo. Most made no protest, but some were outraged at the brutal forced labor system...

And they reported what they saw: children and adults who had hands and feet cut off; murder; rape. Ultimately, Leopold's hold in the Congo would end, but not until he had made over one billion dollars, and reduced the population by 50 percent. If only the missionaries had had any real power, the devastation in the Congo might not have been so horrible.