Head had several opportunities to be a peaceful protester and avoid taking part in the violence, but he’s seen on video assaulting Fanone. Sentencing him to a near-max term will hopefully send a message to future election deniers that things like this can never happen again and that there will be serious consequences for violent actions.
Head's actions may have been inexcusable, but the Democrats are waging war on dissent, and that extends beyond Trump to his supporters who have serious questions about the integrity of the 2020 election. Just like authoritarian countries such as China, they've attempted to silence them by going after their livelihoods and even prosecuting them. They're not just going after one man for assault, but an entire political faction.