I think it's okay to simply pan everything to the center, do your mixing and volume levels, etc. Render it all in stereo and your mono sound system, powered speaker, keyboard amp, or PA will take care of summing to mono. Especially if you are doing your mixes with only one speaker or with a system that is in mono mode.
This way no matter what type of connection you make to your live system, stereo headphone cable, XLR, 1/4" jack, Stereo RCA, BlueTooth, it won't matter as long as your channel strips pan/balance is in the middle. You'll get the same result if you plug in your mono speaker to either left or right output of your mixer if was all mixed in mono (all panning in center during mixing).
Even if you use a stereo live mixer if you only connect one speaker to left or right everything is in the middle so I don't see how it would matter at all.

Does anyone dissagree?

Does the noise in your head bother me ?