Marvel Comics - with one line that you carelessly failed to edit out of the script for the Avengers movie, you have insulted adopted children, adult adoptees, and adoptive parents!
In your new movie, The Avengers, the character Black Widow says "He (Loki) killed 80 people in 2 days." Then the Thor character replies, "He's adopted."
Sooo..according to your scriptwriter, the fact he was adopted is the reason he is a bad guy!
Being adopted is NOT something to use for the butt of jokes! Marvel, immediately cease using adoption as the butt of jokes AND issue a public apology to the adoption community!
These bloggers - and commenters - have already voiced their objections:
http://73adoptee.blogspot.com/2012/05/avengers-why-is-making-fun-of-adoption.html (adult adoptee)
http://adoption.about.com/b/2012/05/04/the-avengers-movie-offends-some-adoptees.htm (About.com guide to adoption)
http://www.rageagainsttheminivan.com/2012/05/avengers-review-for-parents.html (adoptive parent)
http://www.ofmasksandmen.blogspot.com/2012/05/why-joss-why-avengers-spoilers.html (adoptive parent)
http://communities.washingtontimes.com/neighborhood/red-thread-adoptive-family-forum/2012/may/17/avengers-attack-adopted-children-mean-and-unfunny/ (adoptive parent)
In addition, Disney's own boards have an active discussion, "Disney, Adoption, and the Avengers:" http://www.disboards.com/showthread.php?t=2922029
Update: Some people think this petition is calling for a boycott. It is NOT calling for a boycott. In fact, I saw the movie (and it is a good movie, so don't miss it just because of this joke). I am merely requesting an apology from Marvel and asking that they permanently stop using adoption as the punch line of a joke.
Furthermore, you have to consider how children think. A child doesn't know the history of Thor and Loki. Plus, a child does not understand context the same way adults do. A child who is adopted only hears those lines above. So the child thinks to themselves, "I'm adopted. The bad guy was adopted too. Does that mean I am bad too?" One parent actually posted a comment along these lines on a certain forum, stating that their adopted child had actually made a very similar statement after seeing the movie. This statement is now posted under petition updates.