In general I would agree with TBone.
A couple of points I would disagree with, though. Mostly it is not a problem taking photos of locals, but it is advisable to ask their permission.
The point I would strongly disagree with is to use all-inclusive resorts like Sandals. They are a blight upon the Caribbean. They put huge compounds up, fill them with rich tourists, and encourage them never to venture out into the island. They are rarely staffed with locals, and the profit from them leaves the island. Therefore, their island hosts benefit little from their presence. What's more, people who go there do not see the real Caribbean. St. Lucia is a really beautiful island, the locals extremely friendly and helpful, and it would be such a pity not to see the place in all its vibrant, colourful glory. If I had my way, such leeches as Sandals would be forever banned.
However, as TBone says, this is a third-world place. Going around with huge displays of wealth hanging around your neck or on your wrist is, at best, tactless, and at worst, a stupid temptation to put in people's way.
As for that Telegraph report, I can't imagine what caused them to do that - every Caribbean Island I know has a very tolerant attitude to any particular religion, or to people having none. There is a huge mix of religions everywhere, from Catholic to Baptist to Revivalist Evangelical, to Islam, Hinduism, Judaism and varieties based on whatever their ancestors practices back in Africa. Voodoo still has quite a hold in some places, but is harmless. Don't believe what you saw of it in the James Bond movie!
St. Lucia's tourist industry is, thankfully, not as over-blown as that of, say, Trinidad, Jamaica or Barbados. I know of places in Trinidad where, if you have a puncture in your car, you don't stop to change the wheel - you drive home on a flat tyre.
A few years ago Antigua had a widely-reported case of a yacht-owner and his family being hacked to death in their sleep. Thankfully, crimes like this are extremely rare.
As TBone says, a must-see place. But take elementary precautions, remember that these people are poor. When I was working in St. Vincent, I was earning US$2,000 a month. Work it out - and I was among the top 10% of earners on the island!