How do I convince my parents to let me have a facebook?

[Happiness]

you don't say what they have against it, but here are some ideas:

Facebook is extremely useful for keeping in contact with people in group projects. it's pretty much the most efficient way to do it, and if you don't have a facebook it is likely you won't know what is going with the group.

Facebook is a social tool and friends are important. it's important to keep in touch.

if they are worried that you'll get in trouble using it, let them know it's really easy to set up privacy settings so creepers can't find you.

tell them they could get one as well if they want.