Pretend
An often-repeated maxim nowadays is "kink is about playing pretend". This is usually in service of explaining things like why petplay is not zoophilia (its participants don't want to have sex with an actual dog) or why people have kinks that involve a lack of consent (they want to PRETEND they're being raped, they're not ACTUALLY being raped).
While I do not consider this a harmful notion, and it is certainly applicable to a large amount of kink, I also feel it is incomplete and should not be taken as the entire story of what kink is.
Sometimes, kink is an expression of affection or attraction in an intimate relationship, but some aspect of the identities of the individuals involved is expressed in ways that would be considered atypical or kinky.
For example, our system has many therians who enjoy petplay and where petplay as their theriotypes is an important element of their romantic relationships. They turn into animals in headspace, and while they don't have sex in their animal forms, they still participate in non-sexual petplay this way.
For some petplayers, petplay is entirely about playing pretend and indulging in an imaginary scenario in which you are a pet who is cared for, does not have responsibilities, or other fantasies that draw others to the kink. For many members of my system, however, being a pet is an expression of a fundamental fact about themselves and their identity as non-human.
By the same token, much of my fetishization of weight gain and transition fit into the camp of kinks that are not about playing pretend. It's true that some of my engagement with those kinks IS about pretend - I think about gaining more weight than I intend to gain in real life, I fantasize about transitioning in ways or to genders I don't intend to transition to in reality - but where it comes to our body's actual weight and transition, we feel these things genuinely make us more attractive. In many cases, our kinks relating to these things are about eroticitizing our reality and who we really are.
Some kinks are about a mix of pretend and reality. For example, I am a masochist with a fear kink. I gain physical gratification from pain and emotional gratification from fear. I do not enjoy ALL pain or fear, but I do enjoy these things in controlled environments and in activities that are part of an intimate relationship.
In the service of gratifying my masochism and fear kinks, I would want to engage in kinks where someone consensually beat me or cut me while threatening to murder me, potentially even simulating the moment of the killing.
I do not want to be murdered and tortured in real life. This part of the kink is about pretend. If I were doing this kink over the internet over text roleplay, it WOULD be entirely pretend. However, I can also do this kink with people in person, and if I did, the pain would be very much real, as would likely be the fear. Having control over these things via consent and safewords does not diminish their presence.
While I don't think it's accurate to say that it's HARMFUL to say that kink is about playing pretend, I do feel it can potentially contribute to some misconceptions about kink when treated like it's the end of the story.
For example, on the current-day internet, it is very common to believe that everything in the world fits neatly into the categories of "fiction" and "reality" and that these two categories never mix. These people usually slot kink into the "fiction" part of this binary. This usually comes up in communities whose primary engagement with kink is, in fact, through literal fiction - writing or art - and who may not engage in kink offline, or even online with other people.
In my experiences in these communities, they have found it difficult to take it seriously when someone has actual violent kink attraction to a real life person. They therefore do not take it as seriously when someone expresses concerns about safely doing BDSM in real life.
When posing some of my questions to online communities that I am no longer in, about what I should do about my kink attraction to someone I knew from offline, they treated it more like I was asking for advice on how to write a story (e.g. treating it like the other party's consent was a plot point within my control) than that I was trying to navigate an actual interpersonal relationship.
On one hand, the fiction/reality binary that pervades a lot of online kink-oriented communities may stem from different sources than JUST the maxim of "kink is about playing pretend". On the other hand, this maxim, which is accepted by the communities that struggle to see extreme kink as a thing that happens in reality, likely contributes to their difficulty in taking real situations seriously.
At the end of the day, I find "kink is about playing pretend" to be a more useful than harmful notion, as I would prefer that people started from a position of assuming that all my extreme or controversial kink is about purely imaginary things, rather than have them assume all of my kink desires perfectly reflect what I intend to do in reality.
However, it is also, at best, a notion that should accompany deeper discussions about how kink is a part of reality and how kink reflects reality. It is, at worst, a misconception that causes people to ignore the breadth of what kink can be, or that can even result in grave misunderstandings of what is and is not reality.