You do know there’s a big difference between a “default” option and a “mandatory” setting, right? Specifically that you do, in fact, have a choice to change a default?
Not forcing the user to proactively make a choice is not the same thing as denying the user the ability to choose.
Are they? It literally points out “Who you voted for is secret” on the ad, right above where it says that people will know if you voted.