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Speaking about the US:
1) Forced taxation of its citizen is in and of itself unconstitutional, i.e. in the US, it is illegal for the government to force its citizens to pay taxes just because they are in the US.
No.
2) However, the law states that all citizens must file a tax return. It is illegal to not file a tax return, i.e. all citizens are forced to file a return.
3) In effect, failure to file is illegal (punished constitutionally) in order to in force taxation (unconstitutionally).
Stop listening to batshit crazies from the intertubes. Do you really think you're the first to think of "it's unconstitutional" argument, snowflake?