Using "Rather" to start a sentence

I would like to know if "Rather" (not "Rather than") can be used to start a sentence. For example, is the following a good style?

The existence of all those licensed firearms and of so much Protestant military expertise does not justify the republican refusal to decommission. But it does help to explain why your average Falls Road Catholic does not view the IRA's arsenal as a dagger held at the throat of democracy. Rather, nationalists tend to see it as a modest defence against all those other potentially hostile guns out there.

How about this?

It's not that his predecessor wasn't supportive, rather the take-over distracted him somewhat.

And this?

No, rather, it’s that Google did a better job at simplifying the interface than you did.

Should "or rather" or "but rather" be used instead of "rather" in the second example? Is a comma required after "rather".