what is stopping scientists from modifying
 

our DNA? EXAMPLES:

modify our DNA so everyone has good vision
modify our DNA so no one is born crippled or retarded
modify our DNA so people are more intelligent

what is stopping science from doing this other than potential moral and religious reasons?

You can't just "modify" all the DNA in a person's body. It doesn't work like that.

easier said than done......well for one thing DNA is very complicated. DNA is like reading every book ever written and looking for a specific sentence to change. And if you do find that sentence it may take years of research to find out what changing that sentence might do and all the possible problems and outcomes. I hope I could help.

Who says there not, as far as I know they are, but it will probably be awhile before anything comes out of it.