@KJIJH the reason he is dangerous are not his servants. He determined the MC as dangerous because his conections and they know nothing about him which should be impossible and it only ends up in one of the following endings:
1. Some powerful and/or inflentual people/organisation is backing the MC up and concealing information for a reason. Going after him and recruiting him means basically picking a fight with these people.
2. He has Emerald Sword as his friends and this can/will cause political backlash if they decide to leave the country or the hard earned trust gets destroyed because of that. It basically means going against the royal family and high ranking nobles. Basically a declaration of rebellion in the worst case for this young noble.
3. He himself has enough power to conceal it and have some form of (evil) agenda (which is implied by having multiple familiars and how he acts).
Because they dont know much, the MC is a dangerous card which can mean destruction in multiple ways for this noble family.
Thats why I dont like this trope, because that is too stupid and is only acceptable in a rather joke-story. Just because the young noble is greedy to get someone who appears to be "valuable" and he wants the familiars.