I think it's the fact that nearly all the forms of ID are ones that you acquire as you get older, and therefore younger people voting for the first time could be excluded. Voter ID per se I don't have a particular problem with, although other viewpoints are available, but if you are going to have it, have a standard ID card that is issued to everybody over the age of 18. (Is it 16 in Scotland?)
I'm not sure that is true and I'm sure somewhere I saw research suggesting that the people most likely not to have ID are the very elderly, those that no longer drive and have a passport that has lapsed as they no longer travel much.
Actually my experience is that young people tend to have ID and tend to have it on them, as they need it to get into bars etc. I virtually never have photo ID on me, my 24 and 21 year old kids always do.
I agree with you that we should have a standard ID card for everyone - many other countries do and I don't hear much complaint about big brother. The other benefit is that it would help to determine who is in the country legally and illegally. Our crazy country is one where we seem obsessed with immigration, yet have no sensible way to count it nor to determine who is and who is not allowed to be here.