Although he did not say it outright, Marco felt that Sloane would be able to understand the meaning behind his words.
Sloane was in a position as a leader, and he needed to establish a certain role in his group that made his position well-known so that others could follow him.
If he got too close to them or acted like friends most of the time, then it was likely that he would lose the respect of those around him and that it would be difficult to maintain control over them and keep them in line.
It was the same when it came to being taken advantage of.
If they had no respect for him, then they could just use him for all he was worth before throwing him away.
There had been many promising talents who risked themselves for their allies or for the organization they served, but they were not rewarded for it and were taken for granted.