@thing-N-ghost,
Yumclock: despite the fact that currently, if we exist as we exist currently for the entire duration of the existence of the universe, it is possible that two beings with the exact DNA sequences may exist... first of all there is the whole nature v. nurture argument, where - through environmental/cultural/social/technological differences - two people with the same DNA would be extremely different. This is the same argument that people use in response to the morality of cloning (in terms of, would you clone your best friend/mom/dad/significant other if they died so that you could have them back.)
Second of all, DNA is constantly changing. This is shown through the recombination of DNA during sexual reproduction, where some traits will die out, and others will form... even the genetic disorders (for example, Huntington's, Alzheimer's...) that affect our genes change with each generation. Therefore it is not possible for two people to have exactly identical DNA. There will be at
least one base difference.
I digress. Possible for people to truly agree on something? Yes. If they are of the same opinion, even if they have different motivations, then they are agreeing. Actually, the combinations of their opinions would create a stronger argument toward their opinion. Also, there are some that agree without verbalizing. The likelihood that there are at least two people amongst a large group that agree, even if one agrees without verbalizing, is great.
Point: it's a matter of opinion.