Does the SNP really want a free, democratic, Scotland? If so they are everything they can to ensure it may, just, become independent but is unlikely to be a genuine democracy.
Consider the following scenario: the SNP Government imposes a referendum on their terms, with their question and to their timetable. No other Scottish political party agrees not just with independence, but protest that the SNP is rigging the ballot. No effort is made by the SNP to gain agreement about the process.
Assuming they won, which is highly doubtful, what would the result be?
First, most opposition parties would be a best reluctant particpants in the new polity and could quite reasonably become rather like nationalists and republicans in Northern Ireland - parties that simply do not accept the legitimacy of the state they are forced to operate in.
Second, even if they accepted the new regime, they would forever be branded as disployal because of their opposition to independence. This would likely produce a situation not unlike South Africa, where the almost unchallengeable position of the ANC is now undermining democracy.
Far-fetched? Possiblly, but unless the SNP changes tactics and seeks to gain a consensus amongst Scottish political parties and civil society about how to handle the independence referendum there is clearly a danger that might be where Scotland is headed.
Personally, I think it is entirely up to the Scottish people whether or not they remain in the Union. I hope they do, but if they don't fair enough and good luck to them.
Instead of trying impose their will on the (current) minority parties they should immediately establish some sort of independent commission of trustworthy people, agreed between all the parties, to oversee what they are clearly entitled to because of their electoral mandate - a free and fair referendum on independence. What their electoral success does not entitle them to is elective dictatorship about when, where and how such a ballot should take place.