How scientific is it to observe something in a very localized area and the extrapolate that this observation is true throughout an entire planet or Universe?
That isn't what happened.
In fact, science once thought that the milky way was the entire universe and science thought that the universe was static.
It is very scientific to extrapolate theories based on what is known at the time, that turn out to be wrong.
And it is also very scientific to revise those theories as additionall information manifests.
If I note what I consider is expansion occurring around my planet can I then extrapolate from that, that expansion is occurring through out the Universe? Is that scientific?
Yes it is.
Assuming you're humble enough to recognize that you might have to rethink your theory in light of additional data.
It's called scientific method and its served us fairly well.
You got a better system?
Oh yeah, that's right...you've decided to take your cosmology theories from the musings of pre-iron-age shepherds.
Very enlightened.