There is a Biblical commandment to stand before the wise or elderly. Nevertheless, one full of sins is considered to have forfeited his honor and one is therefore absolved of the requirement to stand before such a person (Sefer HaHinukh, Mizwah 257).
Let's assume a large percentage of a given population either conspires to, aides to or gives support to killing Jews (e.g. publicly honors those who kill Jews).
If a Jew sees an elderly person from said population - but, is not certain that that individual conspires to, aids to or gives support to killing Jews - is he (the Jew) required to stand in front of such an elderly person?