If you actually think about it, the old excuse for abuse, heavy rust, etc. because guns were used as tools is kind of dumb.
There are all kinds of tools. Some are designed to be roughly used and abused, such as cold chisels and shovels. They are relatively cheap and expendable to a degree. You sharpen them and use them until they are worn out. Even that type of expendable tool can be abused and prematurely ruined if not used and cared for properly. Only a complete idiot would treat a good micrometer or vernier caliper as roughly and indifferently as a cold chisel or a shovel, but some guys do.... because they are idiots.
Even cheap guns are built with a degree of precision, and they require proper care and maintenance. A friend recently showed me a set of expensive self-feed wood boring bits. Every one was severely beat up and they were totally ruined. I asked him what the hell happened to them. He said he had loaned them to another friend, and they were returned in that condition after he tried drilling through a concrete block wall, destroying one after another while running electrical conduit in his business. Then he told me about other tools that this guy has ruined. He had no brains, and no shame either, to return them in that condition.
I have a cheap Savage model 94 20 gauge that I keep in my garage. I paid around $25.00 for it and had to make a new firing pin. It sits in my unheated garage, ready for use, with a piece of tape over the muzzle to keep mud dauber wasps from building a nest in the barrel. It is a tool, nothing more. But I still wipe it down from time to time with an oily cloth, and check the bore. It is in the same condition as it was when I first fixed it 25 years ago. Some people abuse guns for the same reasons they abuse tools, cars, trucks, and everything else. They just don't give a crap.
