As someone who lives in a country that faced a 20 years dictatorship ~courtesy of the USA~ when someone threatens dictatorship you best believe them.
And if you don’t know what that means, in general lines: you won’t be able to vote, you won’t to be able to exercise the right of free speech especially when it comes to the government, music, art and literature may be banned especially when they are critical towards the government, people may be exiled or killed and they will make it look like suicide or an accident or straight up own up to it.
So do yourself a favor and vote. Brazil has dealt with multiple dictatorships (one of which was military) and I can guarantee you don’t want to know what that’s like.