Regarding Mr Klaus - active or statutory rapist? Since we only know the little that Haley has revealed post coitus I see three possible scenarios: Haley initiated the encounter (exactly as she believes) mainly as a comfort thing that developed into mutually agreed upon sex (in a 'moment of weakness' on the teacher's part due to his emotional state); Haley initiated the encounter only as a comfort thing that was twisted by Klaus into sex (the classic "she was asking for it" response of the rapist, which young Haley buys due to shame and victim guilt); or Haley was completely groomed, manipulated and gaslighted by Klaus into believing she was responsible. The first is the least reprehensible, and somewhat more understandable (frankly I doubt I would be able to resist Haley any time, any where !) unless, as
spooge_nugget points out, it became (as seems the case from Haley's after class tutoring comment) an ongoing relationship. Any teacher should know better (my best friend is a teacher and he says they are trained, and cautioned against such things, even the perception of which are an ever present concern). If either of the latter are true (they would be the least interesting options for me) then Klaus is simply a villain and Haley a victim, which does the character a great disservice.
So do we have any evidence one way or another ? Well, most people believe that the mother knows about Haley's relationship with Klaus, and it would certainly explain her odd attitude - her lack of faith in Haley's judgement and the advice to stay close to MC. If so, then this leans towards the mutual sex option (or at least that Haley has convinced Mom that it was a genuine relationship) since otherwise, without knowing any extenuating circumstances, I believe she would have taken legal action against the teacher. Speaking as a parent, if Haley's situation occurred with my daughter nothing (short of what I considered a serious threat of suicide from her if I acted) would prevent me doing everything in my power to ensure Klaus was imprisoned in a sex offenders cell. Because, as with infidelity, if a person is capable of doing something once they are capable of doing that same thing again, and if that happened I would be partly responsible through inaction (and, yes, revenge hate would play a part, too).
Two things, however, make me believe that one of the abuse scenarios are more likely. Firstly, there is Haley's insistence that she can take no responsibility for initiating a sexual relationship with MC. Previously, I had viewed this as a touch of moral cowardice on her part, but with the Klaus revelation some parallels become apparent between her relationship with Klaus and one with MC: Klaus was also a figure known to the family, whom she presumably respected, and both relationships would have met with disapproval (to say the least) and were illegal. If she initiated a sexual encounter with Klaus that resulted in traumatic abuse then I can finally understand her abrogation of responsibility.
Secondly, there is Klaus' step-daughter (about whom MC wonders). Now, it may just be the use of limited resources, but to me she looks, apart from the hair, exactly like one of the prostitutes that Lisa auditioned, down to the mole on her chin and nose freckles. And one of the classic reasons for becoming a prostitute is abuse. If a person is capable...etc.
Segnbora has made the very valid argument that any action taken in response to the Klaus situation should be determined by Haley, and what is best for her. However, I think it possible that she is already taking that action. The actual Klaus reveal, straight after Haley and MC finally consummate their love, seems so badly timed that there
must be a story reason for it (actually I think it was poorly handled anyway; IMO the update should have ended straight after the sex so that people could savour the moment instead of, for many, tainting it). Haley has a very manipulative side to her (she can basically twist MC round her little finger and has turned him from innocent brother to full incestuous lover within a relatively short period of time, after all), she knows MC better than anyone, how he thinks and reacts, so consider this. It is Haley who insists on visiting the school, the only room we see is the girls' toilet (I mean who would visit that!) and the result is we get the story of $20 BJ Tina, which Haley later uses as the excuse to talk about her past lovers. I think it possible that Haley planned both uncharacteristically hurtful reveals deliberately (her expression only changes once when talking of Klaus, to a strange smile when she says she didn't tell him to make him angry, implying she had a definite motive) to prompt MC into action against Klaus. That Haley, deciding to have no secrets, has turned to her beloved brother, who was always otherwise there for her, and took the punishments for her actions (as she herself says) to deal with the unresolved Klaus trauma, trusting him to act for her.