"They" is a plural pronoun, and here it must refer to one of the two groups of people. In context it must be the second group "those who don’t really want it at all".
When you say "Admit /something/" the something is the statement. Here it must be the thing that "They" can't say. "It" refers to "not really wanting it it".
This kind of strict analysis is not really how language is understood by native speakers. In particular the meaning of "it" is not very important. But the verb "admit" needs to be followed by an object, so "it" will fill that need.