From someone who lived in Utah for 20+ years and whose stepfamily are all Mormon, I wouldn't think of tolerance as one of the faith's defining characteristics.
Although the intolerance often manifests itself as the kind of fake niceness found in movies when an old lady character needs to belittle someone with a sweet smile or calmly shut them out of polite society, not the fire breathing intolerance that wants to wage holy war.
I'd say its mostly just majority in-group dynamics that you'd find anywhere that a majority shared any characteristic. That combined with well intentioned missionary zeal will of course cause issues.
That said, the Salt Lake Valley is now under 50% LDS- the previous Mayor is Lesbian and its pretty progressive generally.
Although the intolerance often manifests itself as the kind of fake niceness found in movies when an old lady character needs to belittle someone with a sweet smile or calmly shut them out of polite society, not the fire breathing intolerance that wants to wage holy war.