Forgive me for not quoting specifically - I’ll see if I can take this one point at a time and give some clarity, for those asking for it. 
Re: consent. Yes, you can construe “if she’s not in the mood, tough” as marital rape, if you desire. However, I believe that her continued willingness to engage with him in a D/s capacity negates that connotation. Put simply, she has the ability (and the responsibility) to communicate to him when she cannot or will not be obedient to his wishes. Because this is a relationship based on love and consent, I think we can safely presume that he has no desire to rape her, in the sense that he would engage in intercourse that would be harmful to her physically or psychologically. That, I think, is a different animal than using her expression of obedience to both their benefit. Believe it or not, some people get off on being used for someone else’s pleasure, so even if they’re “not in the mood,” they’re still getting something out of the experience. Marital rape, in my mind, is in a different category all together - because, given the choice, the person being raped would choose not to be. By remaining with him, and not communicating to him that she is going to be damaged (physically, psychologically, spiritually, or otherwise) by this or that act, she is continuing to give consent to his use of her in the ways he deems fit. By allowing him to call the shots, she is saying that she would rather have sex when she’s not in the mood than see him unhappy because of her disobedience, and I don’t fault her for that.
Yes, you can take some of those sentences out of context and make the argument that they condone marital rape. That would be ignoring the basic premise that they are a loving couple, who each want the other to be happy and fulfilled. It is that presumption which allows all the other things to follow, and it is a presumption that I believe is correct.
To give you an example (which Robin has already referred to): he doesn’t enjoy being tickled. He, in fact, really hates being tickled - to the point where he will physically fight me to get me to stop doing it to him. However, it also pushes a good hot button for him, and a tickling session can make him feel pleasantly used and fulfilled for hours or days afterward. You can certainly make a case that me physically restraining him and tickling him looks like humiliation and abuse. However, I don’t believe (and nor does he) that it is damaging or abusive in any way. I am not saying that this is the case with freekalette and tickling, because I don’t know. I am saying that things that look like abuse without context are not necessarily so.
Re: the difference for the children of an abusive relationship vs. a consensual relationship. I do not have peer-reviewed studies to back up the following, as it is based on my personal experiences (in my own home life and seeing in-depth the home lives of others). Abusive relationships lead to unhappy people - the abused person is generally extremely unhappy, and the abuser is often unhappy as well. Consensual relationships, by and large, lead to happy people - because if the people involved aren’t happy, they’ll leave. I think that, barring some extreme examples (beating her black and blue in front of the kids, etc), the specific kink-related behaviors are much less important than the fact that Mommy and Daddy are both happy and in love with each other. When you add in the fact that they are aware of how unorthodox they are, and therefore go to some lengths to mitigate the effects that specific behaviors may have, you come up with an overall very positive effect.j
Re: the tickling particularly. I will admit to a bias on this, because I enjoy tickling Robin.
However, I think that it’s being cast in a much more sinister light than is deserved. Yes, if it does emotional damage to her or drives her to tears (the unhappy kind, not the laugh-too-much kind) or heart palpitations, then there’s something bad going on. However, I think it’s likely that it’s more in the spirit of a game - “let’s make Mommy laugh until she says uncle!” sort of thing. Yes, if it’s done too often or in the wrong context, it might send a bad message. But again, they’re communicating with their children. And, frankly, I’m willing to bet that there’s been at least one time where it’s gone too far, and she’s gotten genuinely upset, and he’s stopped. I think that it’s much more likely that they will have a discussion about boundaries and what is and is not appropriate with other folks than that they’ll simply assume their kids will “just know” what is and isn’t appropriate.
That’s the thing that I think most people are just not picking up on - no, he doesn’t have to stop. But he loves her, and so he’s going to stop even though he doesn’t have to! I think maybe some folks are taking the “power corrupts, absolute power corrupts absolutely” thing a little too seriously.
Re: the “vanilla” slur. Yes, it gets tossed around too easily and too often, rather than trying to have a productive discussion. It may be helpful to realize, though, that slurs and insults are being thrown on both sides, and are equally productive on both sides. It sometimes becomes hard to have a polite conversation when the tone of question is much more “prove that you’re not criminal psychopaths” than “I don’t get it - can you explain?”
And, anecdotes that are not data: to date, I have met a little over a dozen children and young adults who have been raised or are being raised by overtly kinky people. They have, without exception, been perceptive, respectful, intelligent people. My opinion is that having parents who have carefully negotiated their boundaries and preferences in the context of a loving relationship is beneficial, not detrimental. I think that the assumption that the children will pick up on all the negative aspects of the relationship while somehow whooshing by the positives is unnecessarily pessimistic. Yes, they’ll get some of both - but with care, attention, and a willingness to communicate (which kinky people must have, in order to get and keep a partner), the positives are quite likely to outweigh the negatives.