Should top Marginal income tax rate exceed 50%

[parochial boy]

The answer is almost certainly "it depends". For exampe, a transparent system used to calculate taxable income, and transparency over spending requirements tends to allow for more effective collection of taxes, surprisingly...

It is also the case that lots of OECD countries have various Social Security type taxes that are paid, at varying rates, on your income. And in addition, quite how you calculate income varies from country to country, which can have quite a big impact on what the nominal marginal rate actually is.

[parochial boy]

Of course. The only worthwhile question is whether it should exceed 100%. I'm open to arguments about that.

Exceed 100%? Why on earth? 100% (or even 90% for that matter) would do enough to discourage people from earning a sh**tload of money and I can understand that from a socialist point of view, but letting it exceed 100% would even scare off people who're just genuinely passionate about their work.

Would presumably be used precisely to disincentivise certain types of work/behaviour. Like if you taxed certain types of capital gains (repatriated cash where you can't identify the source, for instance) as income and as as capital gain in order to dissuade tax avoidance.

Marginal rates over 100% can and do exist. Like, in quite a few countries you can wind up paying over 100% if you make excessive pensions contributions (presumably to stop people using pension pots as a means to avoid taxes); and famously Astrid Lindgren had a 102% marginal rate at one point as a self-employed person in Sweden had to pay both income tax and employer's social security contribitions.