Self-Replication is not commercially viable
The OP is right about one thing; what made life so abundant on this planet wasn't intelligence, it was the ability to replicate. Eventually (through evolution) variations in that replication occur and some are advantageous for living in the environment, some are not.
If DNA wasn't so good at replicating itself, life wouldn't exist on Earth, or anywhere else.
This is no different to (say) computer virii. The reason they still exist is their ability to replicate. What they do after that is determined by the payload of the virus (or worm, or trojan, or whatever) but without the ability to replicate, they're not really of any use to the person writing them.
That is ultimately why machine replication doesn't make sense; machines are manufactured to be useful in an applied sense, not successful in their ability to reproduce. To put this another way, you might have the most efficient manufacturing process on the planet (including self-replication) for your widget, but if no-one has a use for it, then the widget won't be manufactured.
While life has become successful because of its initial bias towards replication, humans have become successful because we are 'useful'. We can organise ourselves to achieve far more as a group than we could as a collection of individuals which means that we can focus on replication for only part of our existence (if the internet is anything to go by, some of us focus on it far more than we should to be useful to our society, but that is out of scope here). Machines, our products, will follow that philosophy as humans look at everything around them (including their own inventions) from a perspective of usefulness.
In short, that means that unless a dumb machine is useful (effective) at something we want done, we're not going to invest in its cheap reproduction (efficient) because to do so doesn't increase its usefulness.
We haven't even touched on the economic issue; do you really want your product self-replicating without some way of;
- monetising the use of the duplicates, and
- protecting the IP from people who want to reverse engineer it?
I'd add to this that a self-replicating factory is a LOT harder than it sounds to create. Factories are made of many different resources; metals, rubber, plastic, glass, etc. They take tremendous amounts of energy to create, and to operate.
I just don't see a factory being capable of mining, smelting, casting and drop forging, growing rubber trees for latex, vulcanising rubber, harvesting silica, making glass from it, fabricating solar panels, wind turbines, nuclear power plants and the like to power all this activity, etc. 'Full Stack' replication isn't viable because of the sheer diversity of activity required to harvest the materials required to facilitate it.
"But wait!" I hear some of you say, "What about Star Trek style replicators? They'd make it possible because all you need is energy, right?"
Wrong. Well, alright, not wrong per se, but impractical. To generate the materials you need from pure energy would take a LOT of energy. In point of fact, the universe already has that kind of technology and metals and the like are being manufactured every single day in special fabricators designed for that very purpose; stars.
Stars like our sun take hydrogen and through fusion, convert it to helium and other heavier elements. This is why it is believed we could well be the first life in the universe; many stars had to die in supernovas before there were sufficient metals and dense elements in the clouds from which the next generation of stars were born. Every element in your body was born in the core of a star.
But not a star the size of our sun.
Our sun isn't big enough to produce most of the elements we need for life, despite the massive amount of energy it produces. Even Gold (which is an essential ingredient in many forms of electronics) can't be born in a normal supernova; it is generally believed that gold can only be produced by two neutron stars (or similar masses) colliding.
If it takes THAT much energy just to produce gold, how much energy do you think a Star Trek style replicator would need to produce all the materials necessary for a factory? You'd need a replicator on the outside of a Dyson sphere surrounding a star the size of Betelgeuse with direct solar energy transfer technology just to consider it.
Bottom line; machines won't self-replicate to the point they get out of control because there's no commercial benefit to it, the diversity of functionality required to go 'full stack' is too broad, and the energy requirements to generate matter from energy directly is just too high. We're FAR more likely to be brought down by a semi-intelligent computer software that replicates itself constantly and renders critical infrastructure (via SCADA infection) non-functional.
Given our reliance on it, software is far more likely to destroy us than hardware. Even stopping fuel distribution by taking down critical pipeline flow monitor control systems could create famine in most major cities within weeks given how far people are from the food sources in today's world. It won't be dumb machines that take us down, it'll be dumb programs.