The problem is, every player would have to receive that one more ban to make it fair across the board. Otherwise, we return to the dark age of league in which the player with multiple ban picks just bans whatever counters them without considering their allies.
This means that up to 20 of the current champion roster would end up banned per match. A team could then ban the top ten performers of any given role, reducing options for players on both teams for that role, especially if the enemy happens to ban another champion of that role.
And not everyone owns every champion.
"I don't own many jungle"
"I don't own many support"
etc.
Is a reoccurring issue in ranked play.
1 ban per player is sufficient. It allows everyone an equal choice in the matter without the potential of completely eliminating options made available to the players.
If you truly feel that there are too many "cancerous picks". Champions that players should be allowed to enjoy because Riot created them for both profit and entertainment. Then you could simply not play the game because then you wouldn't have to worry about ever encountering them again.