Removing ACLs from files... can I do damage?
It depends on the purpose of the file you are removing them from.  Remove them from system files, and you may find a world of pain if you do it wrong or remove from the wrong file.  Your own files, less of a problem.

ACLs are a way of extending the normal permissions system that is used to control access to a file/folder.  Ordinarily the permissions system works by explicitly allowing either read, write or execute permissions against the owner, members of the same group, and other people.  An ACL allows you to extend that by providing exceptions and additions to these normal operations, so a file might be writable by the owner, readable by members of the same group (say Users), but not accessible to anyone else.  However you could drop an ACL in that allowed user Bob write access, even though the standard permissions should only allow him read access through his User grown membership.