Bipolar ADC or Unipolar ADC with summing amplifier?

[Felicitus]

Hi,

not sure if this is a beginners question, and may be more of a philosophical question.

I'm designing a board which measures voltage. To be protected against user error, I decided to make it accept any polarity, thus I need to measure negative voltages as well. Most ADCs I have looked at are unipolar, so I digged into shifting the input voltage by a summing amplifier. The question is:

Should I really use a summing amplifier in order to shift negative voltages into the positive range, or should I use a bipolar ADC?

I have googled quite lots, but most designs I came across don't care about negative voltages at all.

[Rerouter]

if the input impedance changes the sum voltage rises so if its a controlled input device your ok, if its any old voltage not so much