As somebody who was raised in multiple divorce/remarriage situations, the phrase "blended family" has always reminded me of a blender. Yes, a literal blender, like this.
A blender is a machine that takes various soft tissues and liquefies, chops, cuts, etc., with the intent of creating a unique new, whole, thing. It isn't a pleasant process if you happen to be in the role of the blendee. I know that the intent behind "blended family" is to convey something far milder than being put through a blender. It's supposed to serve as a replacement for "step family," which some feel is more harsh or stark.
There is a certain presupposition to the phrase, isn't there? It goes like this: that the blending process will proceed rapidly and smoothly, and will yield a consistent, predictable result. To continue with the cooking analogy, if something can't be blended in a blender we don't even try. Similarly, we don't refer to a smoothie as "blended smoothie." It's the same with other food items. We don't say, "blended bean dip." Either the process works, and therefore "blended" is implied in description, or it doesn't work, and we don't even try it. Isn't "blended" only widely used as an adjective with the word "family?" Can you think of other widely used phrases that use the word "blended" as an adjective? I cannot.
Then there is the idea that "blended families" are formed when an elderly couple marry, and they both have adult children. When these aging parents need care, the adult children must cooperate with each other and this can be difficult. I've heard it argued that it is more difficult than what young children and teen's experience. I don't dispute that it can be difficult, but I feel quite sure that it isn't more difficult. Working together to help aging parents is one thing. Living together under the same roof, being expected to consider your step siblings as the same as full blooded, knowing that your step siblings are spending more time with your natural parent than you are, seeing them call your natural parent "mom" or "dad," and having them disappear forever due to divorce after you've forged emotional bonds with them is something else entirely.
Let's think of the "blended family" in a different way. To continue with the cooking analogy, how about "the folded family?" Blending and folding both incorporate ingredients into a single mass, but they do so in very different ways. When we fold ingredients, we work carefully and slowly. We incorporate them very gently, always by hand and with a soft tool such as a rubber spatula. As this video states, the key to folding is to be gentle:
I am being facetious to make a point—I'd be astonished if the phrase "the folded family" gained any traction. Plus people probably wouldn't understand the cooking analogy without some context. But I think it's important to highlight something about the phrase "blended family." It has an erroneous presupposition–it refers to the desired result while glossing over the process of getting there. By so doing, it sets up an unrealistic expectation of what can be achieved.
Given its current presupposition, it seems to me that "blended family" is a euphemism. Knowing that there are so many difficult and truly painful issues involved in divorce/remarriage situations, maybe we could work together to try to develop a more accurate phrase. I always thought, "step family" was accurate and never had objections to it. I once saw somebody use the phrase, "second family." Having lived through it, I could support that phrase. In the mean time, let's work to bring to light the presupposition of "blended family." If we are successful in this, then the phrase would reflect the process more than the outcome.
I'd consider that an accurate development.