I am assuming that the question is asking why the humans consider Old Major's teachings wrong and evil. This would contrast a little bit with why the pigs once they have become corrupted by power, would find his teachings to be wrong.
As far as the humans are concerned, they didn't know Old Major directly, or have access to his teachings. What they would have been reacting to was the results of what he had to say, so lets take a look at that:
- Whatever goes upon two legs is an enemy--this is sort of self explanatory as to why the men would find it evil...they all walk on two legs!
- Whatever goes upon four legs, or has wings, is a friend--the humans wouldn't have liked this idea because it puts all the animals on the same level, working together, united
- No animals shall wear clothes--I don't see what the humans would care about this
- No animals shall sleep in a bed--Again, wouldn't bother the humans
- No animal shall drink alcohol--This is an indirect swipe at the men, who seem most often to meet at the pub in the town by the farm. The idea of abstaining from drinking would seem quite wrong to them
- No animal shall kill another--A symbol that the animals are united, an idea the farmers are greatly against
- All animals are equal--The humans would have thought this absurd, as some animals are more useful to them than others. Also, the idea of all animals being equal gives the animals dignity and a sense of status that shouldn't belong to beasts.
In addition to these philosophies, Old Major was also the one who remembered the song "Beasts of England," which for much of the book is the animal's national anthem. Here are some lines from that which the humans may have objected to specifically:
"Soon or late the day is coming,
Tyrant Man shall be o'er thrown,
And the fruitful fields of England
Shall be trod by beasts alone."--this is an open call for the animals to revolt and push the humans off the island. The humans would have, of course, thought this idea to be wrong and evil.
So, there you have it. Old Major was trying to promote equality and dignity amongst the animals, and also advocating that they do away with the humans (or at least move them away to some other place.) All of these things would have been seen as "wrong" or "evil" philosophies by the humans who have for centuries been in control of the animals.