There are a number of benefits to a healthy reef. First of all, reefs protect the coastline from erosion. They also provide an enormous habitat for many of the world's sea life. Outside of natural benefits, the reef has a few economic benefit as well. Tourists visit the reefs and dive to explore it providing the country with contributions to the economy.
Reef takes an extremely long time to grow and recover. We are only given so much reef on the ocean floor. The reef is also absolutely essential to the ecosystem of the ocean, and of other complimentary ecosystems. In addition to this, if two thirds of the entire country of Australia are in favor of protecting the reef (with the seriousness of naming the situation a "national emergency"), then without a doubt, legislation is in order in favor of protecting the reef. There is no question, the people want it, nature wants it; if it's reasonably possible, it should be done.
It is a national emergency and if the government has the power to legislate chemicals and stop them from polluting the Great Barrier Reef, than they should do it. They need to do something to stop this great crisis in its tracks and do what is in their power to help.
I'm frankly surprised that chemicals drain into the waters of the Great Barrier Reef. Australia is a large country with swathes of underpopulated areas. Industries need to be moved to those areas and away from natural wonders such as the Reef. Legislation to regulate the effects of pollution without decreasing economic activity may be hard to draft, but the Australian government needs to try.