The SNP started out as a party with good intentions and a passion for a cause (whether you agree with it or not)

That's questionable. They were originally a reaction to bigger government after WWII. The Scottish big fish didn't like swimming in a bigger pond so they decided to try to get their smaller pond back. That's why Labour ended up dominant in Scotland for so long, the SNP split the Tory vote and ended up gifting Labour nearly all the seats under FPTP.

The SNP 'left' is a relatively new thing, and arose as a reaction to New Labour being utter cunts and the lucky circumstance of the solidly social democratic Sturgeon being a protegee of the much more right-wing but successful opportunist, Salmond.

Now that Sturgeon has gone, the splits are out in the open. But they were always, fundamentally, Tory snouts looking for a trough.