"I looked at what I think of as the food chain that led to the financial crisis, which was that you had individual consumers buying houses they couldn't afford, sold to them by realtors and property people who were competing to sell more properties at a higher price and so on. [...] I thought, hang on a second, classic economy theory tells you that a competitive marketplace is superior because competition provides a diversity of products which is good for the consumer, and it also, therefore diversifies risk. And yet, in this instance, competition has led every single one of these companies to copy each other, which had concentrated the risk. And I thought, Wow, that's interesting. That's specifically what's not supposed to happen."
More here.
I don't think this is due to competition alone, though it certainly played a role. The real estate bubble that lead to the financial crisis had multiple causes which combined into a perfect storm.
Clearly competition is essential for a healthy economy. Clearly people tend to be competitive. Clearly unfettered competition leads to some pretty ugly outcomes (Marxism took hold as a response to that). Also as clearly, a categorical pronouncement "competition is toxic" is a poor title for anything posted on a site devoted to rationality.
Not going to read your link, given its loaded title.