Bullet points are a tool and like any tool it can be used well and it can be used poorly. Bullet points are great for displaying an unordered list of items. This is not saying that the order in which they are presented does not matter didactically, only that the content of one does not rely on knowledge of the content of another.
Now how does this relate to posters? I can only speak for myself here, but I rarely read a poster from top to bottom. I will skim bits, I will skip sections I deem less important and I will jump around a lot. This works great with the type of information described above. But bullet points do not create this kind of information, they only signal to me that the provided information is of this type.
That is I think, where a lot of the criticism stems from. If you just write some consecutive paragraphs of text and put a bullet point in front of every one of them, you are actively misleading me, because your layout tells me I can skip around, while the content should be read in order. In turn, if things should be read in order, signal that to me by enumerating them or if need be, by putting them as consecutive paragraphs into some block in your layout.
On the flip-side though, if you can, avoid the latter. Long paragraphs don't work well for the type of reading described above. But this does not mean that you should put bullet points in front of them, but that you should think about, if it is possible to restructure the information usefully in such a way that bullet points (or enumerations) are the best way to display this information. If you can, then maybe do so. If this does not work, then use paragraphs.
tl;dr: Use the right tool for the job, but don't be afraid of changing the job to suit the tool you want to use.