I hope you're not saying plastic in the ocean is better than having it safely disposed of in a landfill. Where exactly is this rich cultivable land that you speak of? Worrying about plastic buried in a landfill is like worrying about a fly that might land on an elephant's ass one day.
Plastic Waste
Plastic products are very common in our modern life. According to estimates, every year we use approximately 1.6 million barrels of oil just for producing plastic water bottles. Plastic waste is one of many types of wastes that take too long to decompose. Normally, plastic items can take up to 1000 years to decompose in landfills. But plastic bags we use in our everyday life take 10-1000 years to decompose, while plastic bottles can take 450 years or more.
Let the singers sing and the dancers dance. We are the best at providing resources and we should excel at it. If we can make heavy industry work that would be great, but unlike the US and Russia (not a great example btw) we do not have a large domestic market to help out.