I’m from the same group as @jamesobutler and have to agree with him that it is annoying that I have to deliberately stop moving my cursor to be able to place fiducials in the 2D views (for segmenting and other operations). I use Slicer not only for analysis, but also for acquiring new image data with robotic imaging hardware. It is common for me to quickly place fiducials in a 2D view that guide the robot where to go. These locations do not have to be precise which is why my cursor might frequently be moving at the time that I click. When I’m imaging there is usually a lot of things going on at once and I want to be as fast as possible and not get thrown off by a fiducial placement getting rejected.
Another observation, the fact that my cursor type is the fiducial placement icon with a fiducial visible at the end of it even while my cursor is moving and then it not doing anything when I click in a 2D view feels like a bug. It’s indicating to me that it can place something, but then silently rejects it which is confusing.
I took a look at other 3D modeling programs (e.g. Solidworks) to get some inspiration on how to deal with simultaneous point placement and view manipulation. It looks like their approach is to not perform any view manipulation with the Left click and keep that action reserved for Tool actions. For example, the 3D Rotation action is performed by the Middle-click, while Pan and 2D-Rotate are accomplished by Ctrl-Middle and Alt-Middle respectively. Slicer currently accomplishes these things with Left-click, Middle-click, and Ctrl-Left.
If it is too drastic of a change to migrate away from Left-click, what about using an Alt-Left when in Point Placement mode? The Alt button appears to be underutilized for these sorts of view manipulations.