The point being, most of the time people say "build consensus", what they mean is either

"let's have an endless, design by committee approach where the backend dev with no knowledge on UI decides how the UI should look rather than letting the UI designer create a few samples and iterate and everyone else giving feedback like a user would"

or

"we already decided this is going to happen, but for the sake of formality we want you to agree with it so we can feel good about ourselves bullshitting one another into believing everyone has a say, so give us the ok or we'll pester you until you do"

It also stimulates the idea that disagreements are inherently wrong and nothing should happen while a disagreement is in place. Sometimes, it's ok to disagree with someone else and see what happens. Some might call this a form of consensus, though I've had managers get uncomfortable when I didn't vehemently agree with the plan, but was willing to keep my nose out of it and focus on my own things so others could take the risk.

There's a third thing they could mean: we want this to succeed in the organization which means we need to both hear people out to reflect their real needs in the plan, and that we need to communicate to them in a way that they buy in. So that it can work.

In fact this is really the only way to get anything done regardless of what you call it.

Yes, this. It's funny seeing so many people being cynical about this - sure, there's plenty of ways for it go to badly, but far more importantly, there are a couple of ways it can go right.

As general commentary - if you're smart and good at identifying problems with things, use your ability to identify problems to avoid those problems, not as an excuse to avoid doing stuff. Being cynical about everything isn't a terrible strategy, as long as you remember that you need to be cynical about your own cynicism, too.