Whether there's a cork or a screw top has little to do with the quality of wine, and more to do with its geography (which I guess some could argue equals quality). There are no cork forests in Australia or New Zealand, and importing corks would be uneconomical. There are plenty of cork forests throughout the Mediterranean Basin.
Ecologically speaking, cork forests host wonderfully diverse ecosystems and are home to many endangered species. Harvesting wine corks uses only the bark of the tree, and does not damage the tree. These trees live for hundreds of years, so by purchasing wine with corks you are economically encouraging the preservation of cork forests. If the market for corks collapsed in favor of screw tops, people in the area would be incentivized to cut down the forests in favor of some other more profitable use of the lands, see, e.g., Rainforest, The. So support the environment and buy wine with corks.
On the other hand, if vineyards in far flung places such as New Zealand and Australia were pressured to use wine corks instead of screw tops for purely aesthetic purposes, they would have to import them which would increase the cost of the wine, and the transportation would significantly increase the carbon footprint of producing each bottle. So support the environment and buy wine with screw tops.
Either way, relax and have a drink.
