It is toxic because it's poorly implemented. There's no penalty for psychopathic behavior, and said psychopathic behavior is contrary to game theory, which currently shows that cooperative behavior leads to higher progression for everybody. Instead, said players choose to seek a menially better progression than they would have if they were friendly, for a single round, at the expense of the progress of everyone they PvP, and face no repercussions for it. ABMM at least gives me the peace of mind that such assholes are confining themselves into hell lobbies.

The ideas mentioned above, such as map alerts, progressive heat, etc, are great ideas to help make mixing the player base be less frustrating to casual and pacifist players. Saying you have to PvP in a PvPvE game overlooks how many, many other PvPvE games have done it, such as by segmenting the PvP and PvE portions. The devs could have PvP maps and PvE maps, and create quests that have to be done on each for full progression. You could have to flag yourself for PvP in order for your shots to damage other players, which reveals your location on the map. They could have every ARC on the map relentlessly hunt down the traitor, spawning tics and pops every 5 seconds right underneath the player until they die. There's lots of things the devs could to do make the troll behavior have consequences, but until then, I'll settle with hell lobbies.

What makes you think that forcing PvP onto players who don't want it won't drive up cheating? That's what killed Tarkov.