Original sentence: IP already does that, therefore, there is often no point in implementing ATM at the network layer.Many ADSL implementations also use ATM.Since there will always be both brand-new and obsolescent link-layer technologies, particularly in the LAN area, not all of them will fit neatly into the synchronous optical networking model for which ATM was designed.Therefore, a protocol is needed to provide a unifying layer over both ATM and non-ATM link layers, as ATM itself cannot fill that role
Edited sentence: Also many ADSL implementations use ATM.Conveniently, we have this protocol called "IP" which already does that.Ergo, there is no point in implementing ATM at the network layer.Many people, particularly in the Internet protocol-design community, considered this vision to be mistaken.Their argument went something like this:  We know that there will always be both brand-new and obsolescent link-layer technologies, particularly in the LAN area, and it is fair to assume that not all of them will fit neatly into the synchronous optical networking model for which ATM was designed.Therefore, some sort of protocol is needed to provide a unifying layer over both ATM and non-ATM link layers, and ATM itself cannot fill that role