Studiot I take your point about reaction force. It's a clever point, and it's undeniably true, but it doesn't really address the common sense "obvious" realworld application of Hooke's law  which is that you hang the (swear) wight, and then you measure the (swear) extension. " (swear)ed" in this case, is a scientific term.

That's a bit strong.
Take a close look at these graphs.
In the first one I have plotted Load against Extension in the conventional manner.
Note that this is a well behaved mathematical function, with the load being
a single value for any given value of extension.
Thus the function described by this graph can be substituted into all sorts of mathematical formulae and procedures without problem.
Now look at the graph drawn the other way round.
I have indicated that points 1 and 2 on the graph have the same value of load, but have different values of extension.
This is the real world that you were so flippant about.
This means that extension as a function of load is not a single valued function and cannot be used in formulae associated with the mechanics of the situation. The example I have already offered you is the work done by the load or the energy stored in the spring.
All real world elastic objects act like this.