Is it wrong to judge how people behaved in the past based on today's morals?

Well, I am not an expert or as good as others on this board in these kind of philosophical matters. My simple view is that there is no good or right thing. It's just a matter of our subjective opinion. You can argue that there are some things such as killing an innocent child, which may be considered almost universally bad. But if a person was to derive pleasure in killing an innocent then that is a good thing for that person. But because we live in a system where we interact with each other and the ideas of good and bad can conflict we establish the concept of goodness or badness through moral codes or formal laws. At end of the day such moral codes (which was initially established by religions/elders/tribes) and formal laws (law of land) ultimately attempt to make our society a safer place to live. But there are always trade-offs.

Recently, I saw a discussion on another board where someone called a famous person anti-Semitic and racist. Another person sharply attacked the first person and said that the society in old days was different so it is not totally fair to judge people of old times according to today's standard. That may be true but there is always a better measure of judging people of past. Judge them in relation to other people of past (contemprorary's).