I suggest you start an external guild chat (Discord is nice), and make it mandatory to join. Discord has notifications, so anything important can be posted and tagged with every guild member.
I believe you had the right idea kicking that player. Truth is, people get unruly once one person gets away with breaking the rules. One person's actions basically just upset 49 other players. It's better to have one slightly disgruntled player, than a whole guild of rightfully upset members.
Once you get the guild chat going on Discord or wherever, you can explain why you kicked that player (although they are likely gone for good at this point), so that everyone knows that it's not okay to break the 0 damage rule. You can make some kind of guideline where you kick a player who scores too early in a match, but reinvite them immediately afterwards. They won't get rewards for the raid, so no one else loses out for the misfire. This obviously has to be tweaked for TB.
Just my two cents. It sounds harsh at first, but down the road you will be glad you put down some basic rules and consequences.