Photography is all about cropping, you select your crop of reality by how you frame your shot, so to then crop into the image in post if you decide it needs it, is simply a continuation of that process.
I always try to crop with the camera when out in the field, but sometimes the scene just doesn't want to fit neatly into the 3:2 aspect ratio I am forced into with the type of camera I use, so I will happily crop in post if I think it improves the image and I feel no guilt by doing so, but as you can see by the vast majority of images I post here on Lula, that I do indeed try to mostly stick with the 3:2 aspect ratio and the image as it was shot in-camera, but this isn't because I feel a need to slavishly follow the 'rules', it is more to do with saving me time and money when framing prints etc, so I can buy and use stock frame sizes rather than custom sizes.
I think this whole cropping in post thing is bunkum if I am honest, photography is an art form and we are supposed to be enjoying ourselves as we pursue it and not treating it as some kind of hairshirt wearing penance. So just go out and enjoy yourself and don't get bogged down by listening to anyone telling you what you must or must not do, do whatever you think is best for you and your photography, be yourself not a rule following robot.
Dave