U.S. income tax returns these days are similar to a credit card company making you report all your charges to them and they don't tell you what they know.  If you miss a charge (1099, etc ) they penalize you.

Other western countries don't do this.  

Plus, forcing you to sign the return under penalty of perjury is unconstitutional under the fifth amendment of self incrimination. 

 If its unconstitutional then why does it exist? 

 Unfortunately lots of unconstitutional things exist these days…. It’s all subjective.  You can not sign and be prosecuted or put potentially incriminating info and be prosecuted.  The rational is “The 5th Amendment is not a license to commit fraud. The right not to testify about your past crimes does not mean that you are allowed to be untruthful in the present.”