You have to keep in mind that Scotland throught it's common history with England and the UK kept sovereignty in some aspect, it's not the same if a unitary state to breaks up or a federation/real union.
That beaing said, the Soveregnty of the Scottish people is in their hands and they can do whatever they want with it:
I don't consider territorial fragmentation any good.
Me neither, gaining independence and then trying to join a union (like the EU) also seems a bit pointless.
It's not pointless.
You need to look at the big picture, now the Scottish policy towards EU is mainly governed by the UK, they can't do as much on the scene with the UK giving oredrs. Of course, it's not that harsh as I may have made it sound but the UK has certanly put some restraints on the Scottish international behaviour.
Breaking up from the UK will bring independence for the Scotts. That's great for them, they can govern themselves and economise with their own resources as they wish.
Applying and joining the EU will make Scotland a sovereign nation, standing AS AN EQUALL beside the UK and the rest of the nations.
That means even when the UK wants something to pass in the EU parliament, the Scotts could block that (Funny, isn't it?
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Some of this story is familiar to me as I'm from Croatia, Yugoslavia broke down and 10-15 years later, we're joining EU, relinquishing some parts of our sovereignty to the EU but that doesn't make us as weak as we were 20-30 years ago. Back then we were a mere federal state in a socialist federation, today a modern, sovereign nation, actually having an impact on the stuff happening on the Continent.
You also mentioned that Spain might veto Scotland?
That's wrong because there are some gread differences from those 2 situations.
Scotland joined freely with England (at least, their parliament voted for the merging) so, in theory, they can break that relation when ever they want.
Catalonia and Baskia (I might've misspelled that, pardon me) are a part of a unitary state, so a quick definition follows (in my own oppinion):
A unitary state is a state in which power is derived from above, so it can only be given temporary to lower organisations but it DOES NOT emanate from them.
So the situation is quite different and Spain might aswell accept Scotland, only to have an aditional leverage against the UK.