Have you ever heard of the idea of starting simple and then adding to it?
Well, that's what I'm trying to do with you. I'm trying to explain using examples that are as simple as possible. I agree that these over simplified examples do not reflect the real world. Guess what. They aren't supposed to. They are an attempt to get the basic idea of inertia across. That's why inertia is Newton's first law - because the second law builds on the first and the third builds on the second.
Mainstream can have the word, inertia but it has to be explained as to what it is an d not just passed off as a property of mass that means absolutely nothing.
You can build on something that does not exist as anything meaningful.
In order to understand inertia in its simplest form, you have to strip away everything until you get to the simplest example - an object at rest with no forces acting upon it. It doesn't matter that this can never happen in the real world. It only matters that you can picture it in your mind and understand that if no forces are applied to that object, then the object will not change what it's doing (just sitting there).
It does matter. It matters a great deal.
It only doesn't matter if we use it as mere fantasy and keep it as that, without even trying to bring any of it into a real life theoretical scientific context.
The fact that we require it to be in real time, means we need to explain it with real life observations and senses.
Now you need to understand that there is never an instance in our lives on/in Earth where we can experience anything completely at rest, because everything is vibrating and vibration is friction.
The same idea for the object in motion. If an imaginary object is in motion and there are no forces acting on it, then why should it stop moving?
If there are no forces acting up on anything then there is no movement or vibration/friction meaning no life, meaning no Earth cell. Nothing.
I think that we may be using different definitions of the word "resistance". To me (and most of the rest of the world), resistance is a force that opposes motion. For example, friction is a common force of resistance. As I said earlier, it is quite common to imagine an environment where there is no friction or any other type of resistance in order to simplify the situation and get the basic point across.
You can't simplify the situation to that extreme fantasy, as I mentioned above.
Friction is resistance no matter how it's brushed up.
One objects resistance is another objects friction.
Energy is friction and vibration and to make energy, something has to be resisted.
For every action no matter what, no matter where...there is always an equal and opposite reaction to that action. Always equal and never more nor less.