With that in mind let's assume I get sued for selling posters of 20 Getty pictures of a celebrity on the red carpet of one event. I do not have a license.
That would, straight up, be twenty counts of infringement right there (assuming these are twenty different photographs and not twenty copies of one photograph); that you would be selling them for profit would leave the door open for a willful infringement claim.
Could't I argue that those pictures are not copyright protected and therefore there can't be an infringement?
You can argue that white is black, up is down, left is right... or that you think that the images aren't protected by copyright. Your opinions will not necessarily be backed up by evidence, facts or law

Surely, it took some skill to take these photos, but creativity? If I see photographers taking pictures at these big events it's all about taking as many pictures as possible and then sorting out those who are sellable. I do understand that some argue that what is worth copying is worth protecting, but I'm missing the creativity requirement in that approach.
I've worked high-profile red carpet events with A-list attendees and you need both skill and creativity. Skill comes in knowing how to set your gear to capture the moment. Creativity comes in the selection of variables to craft a particular aesthetic including, but not limited to, your choice of camera, lens, aperture setting, focal length, ISO, shutter speed... then there's whether you're using on-camera flash, remotely triggered flash, ambient light or some combination of the three. There's the choice on how to frame your subject, the merits of distance-to-subject as regards depth of field and background separation, and a dozen other on-the-fly variables that you have to adjust on account of reacting to an event as opposed to being in a controlled studio environment.
And something else came to my mind: Let's assume those 20 pictures look all more or less the same and were all taken by one photographer.
... we're back at twenty counts of infringement, as this suggests you're selling twenty different posters (or thinking about it)
On the other hand: Let's assume those 20 pictures look all more or less the same and were taken by 20 photographers. Could that open the field for some arguments against protection?
Nope
Could I, for example, say that they all look the same so only one picture can be protected?
Nope
Or could I, for example, say that 19 photographers violated the copyright of the guy who took the first photograph?
Nope, x19.
I have been elbow-to-elbow with other photographers at red carpet events. The chances of anyone using
exactly the same creative choices as I am, at the exact same moment, are so minuscule so as to be practically non-existent. I've looked at the resultant work of some photographers and, in some instances where we
have captured almost exactly the same moment, there are noticeable differences in the frames when you look at them.... and that, right there, is what the courts term 'originality' as pertaining to copyright.
Would it make a difference if the 19 photographers knew how that first picture looked like or didn't know how it looked like?
Trust me. If I'm photographer #1 in this scenario, I really am not thinking or caring about what the other nineteen photographers captured (or didn't capture). My priority is getting images to my client as fast as possible, ensuring they are correctly captioned and have all relevant metadata embedded.
We'll all joke with each other whilst waiting around but, come go time, it's a professional work environment.