Scottish nationalism and English nationalism are two very different beasts. What you're saying is akin to saying anyone who believes in a fairer society is a Stalinst.
English nationalism has developed on the grounds of racial superiority and discrimination, it is about anti-immigration and it breeds bigotry.
The SNP campaign is simply for Scottish independence or, failing that, greater self-governance. There are no extremist undertones and it is owing to the fact that they have traditionally been governed by a different country. Their policies are left of centre and very inoffensive.
You say that no nationalist party should be accepted, totally ignoring the fact that some real extremists who do discriminate based on nationality are also involved (UKIP).