While I agree with you, it's not entirely true that you have one form that you post in once a year. While your 'group certificate' is postcard size, I
think it's somewhat like a W2 (been a while since I received either), you still have to submit a personal tax return. For most people, it's just a case of reporting the information on the Group Certificate(s) (depending on how many jobs you had) and perhaps claiming on some deductions like uniforms or (new) secondary school expenses for dependent children.
That said, the government is talking about moving to a model whereby you don't have to submit a return unless you specifically want to claim some deductions. This is more like the UK model.
As for the US being the laughing stock - I don't know if I would choose those words, but I do think the IRS needs its wings clipped by foreign governments. The whole W8BEN form thing is ridiculous (so tempted to put F.YOU IRS as my contact details) as is the mind-boggling fact that the only way to not file a return in the USA is to renounce your citizenship (and good luck visiting your relatives after that!).
The myriad of local, state and federal taxes, forms, rulings and corporate structures - well, I do wonder how much GDP is lost in paper shuffling. It can't be insignificant.
Personally, I would have the tax laws in most countries scrapped and replaced with flat-banded taxes with zero exemptions. The tax rates would be lower to make up for the lost deductions, but in general, if you earnt X, you'd be up for taxes of Y. Corporations would be kept for their original purpose of limited liability rather than taxation structures. As noted above, it's all the special interests that get in, and, well, anyone who was tried to selectively reward children will know the impossobility of 'fair' once selective rewards and exemptions are introduced.