A good firearms engineer/designer uses the techinque and material that will give the best results at the least cost. No one in his right mind would make a barrel out of polymer, yet it has been proven to perform well as a material for pistol frames, at least for those frames designed for its use.
Likewise, plastic, aluminum alloy, and other materials can be used where some quality, like light weight, makes them superior to steel.
Same with manufacturing techniques. Casting, stamping, machining from solid, MIM, forging, each has its place in modern firearms design. Sure, some materials or techniques have been introduced prematurely or used in unsuitable applications, and that is not good. But insisting that only one material or one method of manufacturing is acceptable often is more the result of blind prejudice and ignorance than of any realistic appraisal and understanding of what is involved.
I once had a man tell me that, "I won't own a gun that is not made from forged steel". He then informed me that one of his favorite guns was a Ruger Mk I .22 automatic. I never told him that his "forged steel" pistol was made from round bar stock, thick-wall tubing, and a stamped out "clamshell" frame.