The Laws of the Game are completely clear on this, and they define careless, reckless, and excessive force. These are used to determine the punishment for an illegal tackle or challenge i.e. free kick only, caution, or sending-off.
In this video, both players were moving towards the ball, but only the goalkeeper had any realistic chance of winning it. The attacker, while moving at much greater speed, threw his head towards the ball and the goalkeeper. The attacker is likely to have known that he had minimal chance of playing the ball fairly, and there was every chance that his head would collect the goalkeeper, probably above the chest. A compounding factor is that once the goalkeeper has the ball in their hands, any challenge, regardless of how it is made, is illegal.
The outcome of this, is that even though he was making some attempt to play the ball, the attacker's head made heavy contact with the goalkeeper's head, solely as a result of the attacker voluntarily committing himself to a challenge that he had minimal chance of winning fairly. The referee decided that this endangered the safety of an opponent, and as per the first paragraph of my answer, this must result in a sending-off.
Contrary to your suggestion, the Laws of the Game do somewhat make a distinction between "on purpose" brute force, and "accidental" brute force, but not in those words.
Law 12 - Fouls and Misconduct, Section 3 - Disciplinary Action:
Serious Foul Play
A tackle or challenge that endangers the safety of an opponent or uses excessive force or brutality must be sanctioned as serious foul play.
Violent conduct is when a player uses or attempts to use excessive force or brutality against an opponent when not challenging for the ball, or against a team-mate, team official, match official, spectator or any other person, regardless of whether contact is made.
Players sent off for violent conduct are typically suspended for much longer than those sent off for serious foul play. This is the distinction. The reason that both offences result in a send-off is because challenges made with excessive force, no matter how accidental, can shorten or even end playing careers.