I can show you hundreds of macro shots taken at 1:2 and 1:4 that you will not be able to tell they were not 1:1. If you have a good lens with macro capabilities (whether it's 1:2 or 1:4), you should be able to get some pretty incredible images. Assuming the camera has enough megapixels and good resolution, one can always crop the image a bit to obtain the 1:1 ratio w/o loss in IQ. But then again, that's just my opinion.
I am well aware that it is possible to achieve Macro photography without the use of a dedicated Macro lens. There are also situations where getting closer to the object may not be practical. In many situations, a dedicated 1:1 macro lens out performs zooming and cropping and other methods.
The fixed focus length in macro lenses usually translates to (much) better sharpness compared to zoom lenses.
To make it clear, I do not discredit anyone making macro photography without using a macro lens. All I am saying is that a macro lens is designed to take macro photography, and it usually performs better.