Normal people have ability to filter out sodium from the bloodstream on high intakes without any problem. They might develop problems with the kidney but kidney problems due to sodium is doubtful. I'd say tea is more dangerous for kidney than sodium. But same does not apply for sugar. If you eat excess sugar it will turn into blood sugar, and it will cause insulin to spike. The body eventually stores the excess in fat, but the process is so harsh for the body that it will definitely cause cardiovascular problems and diabetes.
Sodium is problematic because it makes us easy to eat carbs (i.e. sugar) more. Try to eat excess sodium by itself or with protein or fat. You really can't. But with carb you can. Sodium isn't toxic per se. Carb is the problem. Thus the sugar tax.
Lots of innocent food ingredients have been blamed for cardiovascular disease and diabetes. Fat's been exonerated. But I really dobut that sodium is bad for those two. Fat and sodium have the same thing in common. They make carb taste good.
>frozen prepared foods
As long as they use good quality ingredients it's OK. Taxing them would make them less profitable and result to using worse ingredients.