I wish I were being hyperbolic, but it genuinely isn't the case. I saw someone just this morning change their Facebook status to "voting Conservative". He didn't post any views, didn't try to change anyone else's mind and said nothing. Within an hour the comments section ran into the dozens which ranged from sheer disgust at how he was voting to literally stating that he must not understand what the parties stand for. The levels of condescension and revulsion caused him to delete the entire post within a few hours.
Ridiculous.
What was he expecting to happen?
He posted it intentionally on social media to get a reaction, it just so happens that it seems most of his friends lean towards Labour. If his list leant towards Tories he'd have a comments section full of people applauding his decision. And Vice versa if his voting intention was the opposite.
At the end of the day, he put it up to get either a reaction, or to get attention - and he got that.
If he was so intent letting everyone know that he was fulfilling his civil duties by voting he could have just put that he was voting on his fb, and no one needed to who for.
Or, if he didn't want a reaction he could have no said anything at all.
Social Media is driven by interaction, engagement & visibility. Anything you put out for others to view, like, share, comment on you do with the knowledge that they are free to agree with you, debate with you, share your thoughts & ideas etc.
You can't feign ignorance to this fact.