Earlier quoted context omitted.
Oh nice, your technique could then be used succesfully against ANY voting. Right? Just watching the boots. Because keeping the poor or 30% of population watched at gunpoint 24/7 for 2 weeks in Europe so that nobody notices is perfectly easy.
Not exactly, because of ballot secrecy. Nobody, not even you, can prove what you voted (or didn't vote) with a paper ballot. This is the primary countermeasure against coercion and bribery of the electors. With e-voting, providing ballot secrecy becomes much more complex because at the same time you need to prove that every voted is counted as it was cast.
More importantly, nobody is allowed to enter the voting booth with you. However, there's absentee vote by letter in practically all european voting laws that I'm aware of and that can be used as an attack vector since you can fill it in at home.