I'm a guy with my ear pierced, why do so many people look down on me because of this?

It's effeminate for a man to have earrings. 

that may be the authors perspective based on  THOUGHTS  associations or personal interaction ... ask those  one interacted with  they will  express THEIR  prejudices  and associations  i can not read other peoples thoughts .. that's why people ask questions ..... ask the specific individuals 

its called human psychology  and various CULTURES ... many cultures men engage in ear , nose   piecing  and even religions  promote body modification to  mutilation  such as penis  circumcision  elongated skulls for social status tattoos  neck rings  done for  aesthetics sexual enhancement  traditional symbolism creative art  and shock value   adornment   most common is ear piercing  ..... all about the people you socialize with or live in a community you frequent or work

  PREJUDICE  is a common human reaction or response  RESEARCH  indicates  the following emotions are in play with PREJUDICE   PITY ENVY DISGUST and PRIDE  play a role  and with the out group  its when it goes to HARMING other  its a issue to confront

I have believed for quite a while that men who try to look like women doe not really like women but fight with them. I like men to like like men and women like women! Why would a man try to look like a women? Women look just great the way they were created and I could say the same for men! Does that answer your question?

I don't know your area, but everyday there exists a large group of males of all ages with pierced ears that are accepted as a normal part of society.

I assume you got your piercing initially because you liked it. So why should you care about what other people say or do?

How do you know that they look down on you?

Its probably an unusual thing to see on a male. So much so in fact that they probably think that your deformed and they feel sorry for you.

If they look down on that, that is THEIR problem and NOT yours.

For real reasons, it could be they think that is more of a feminine thing to do, they are judgmental and too set it in their ways, or they may think you are gay or feminine.

There's no good reason though!

They don't, they probably don't even notice you've had it done. People are too busy worrying about their own lives, a small hole in someone ear will be the last thing on their minds. 

No body cares..... no one..... please accept that no one cares