I might actually be able to answer that: toxic overcompetetive players can't be kept out. As soon as a game is of a certain genre, size, design, they flood the game and complain about it being too easy and having no endgame, therefore being dead. Since toxic overcompetetive players dominate all online channels by sheer time spent alone, they raise the impression of being "what gamers want" while actually like being less than 10% of a playerbase.

So far, every single game that started out as casual has become a playground for toxic overcompetetive players over time thanks to this mechanic. Funnily enough, the usual "you can just play something for casual" is usually being used after invading the casual game and demanding it turning more toxic and overcompetetive.

It's so weird playing games like CSGO and seeing two completely opposite sides of the same toxicity. You have the "try hards" that are toxic to the lesser skilled players, and the toxic players that talk shit about people who "try hard." They're not even necessarily talking to or about each other. A player just playing the objective and doing well will be called out as a tryhard, and a player who is doing pretty well and makes one mistake can be berated by his team for being a noob.

Having spoken with so many gamers who behave like this, I have found one common theme among them: They never played sports or team games IRL. Which leads me to believe the real root issue is a complete and total lack of sportsmanship, since video games do absolutely nothing to promote or teach good sportsmanship.

nothing is wrong for having a competitive mindset and therefore beating weaker casual player. The toxic part there is blaming the casual player for being bad like most (not all) tryhards in some communities. What they didn't know, with such a behavior they actively prevent newer player to access the game cause todays casual gamer could be tomorrows competitive player.

Back in the days before SBMM became the norm, you could have fun playing a competitive game without everyone being sweaty. My best gaming memories are of Halo 3 social games. It was still competitive but you rarely got ruined by full teams of hyper-sweaty no lifes. Even if you got put with people a lot better than you, most times they wouldnt just ruin your game, you could communicate through teabagging and just hang out. But now that CSR and loot box rewards etc are on the line, everyone is a hyper sweat and will just continue to dick on you so they can get their next lootbox faster.

A real answer is my spouse plays them. I occasionally try to get into a game they are playing to spend more time together, but it's so toxic it never lasts more than a few nights.

Well I think there are enough games which attract both types of players and there is a lot of friction. Most Blizzard games fall into that category.

World of Warcraft and Overwatch attracted a lot of casual gamers and it is a shame some competitive players give them a hard time.

Taking World of Warcraft as an example, it would actually make more sense for competitive players to play with their guilds only. But many want to use the random dungeon tool additionally, out of lazyness in most cases, and than go ballistic on casuals.

If you can't deal with players being in a dungeon the first time or doing LFR, than don't use the tool...