Historically, it happens time and time again. Anarchist groups are always infiltrated by forces which co-opt their mobility. Sometimes it is by organizations with a lot of money. Sometimes, it is by hard Leftists who wish to turn their autonomous groups into Trotskyite or Leninist cell groups. But it is important to remember that the force which most often co-opts them is their own selfishness.
Many Anarchists are good people. The word really only means one thing, but many people have a different way of interpreting that one thing, which is why you have so much anarcho-something else. Anarchy means 'without rulers.' Without endless hairsplitting as to what constitutes a 'ruler,' we can simply look at the nature of the idea and how it is executed. In radical politics, you earn ontological points for taking an idea as far as you can possibly go. Those who don't have rulers don't believe in power at all, so they end up denying its existence and destroying anyone who is more powerful than they are, no matter how they interpret the nature of that power. The goalpost always changes. You're a statesman? You're the enemy. You own property? That's a monopoly and you're the enemy too. You want to sell a service? No, it should be free and you're also the enemy. You want an identity? You believe in the family unit? You want to be married and build a future? In every case, it can always be said that you have more power than someone else, and anarchism is not very useful to anarchists if it can't act as a leveling force against all of these features of life.
Antifa certainly do not represent all anarchists. Many anarchists have good principles. On the other hand, many of them are resentful parasites. Antifa is simply the ultimate conclusion of anarchism. If everyone above you is a fascist, you will tear everyone down until no one is left. You will use desire as a measuring rod, and whoever has what you do not is the enemy. 'Fascist' for them is a metaphysical category, which means they will never stop finding it. Ideology creates enemies that can never be defeated.
I would oppose to the destructive nihilism of anarchy the active nihilism of autarchy. Autarchy is 'self-rule.' Some could argue that there is literally no difference between no rulers and self rule, but it is a difference of attitude and mindset, and attitude and mindset are what create reality. It seems like a subtle difference at first but, when kept as the goal, autarchy veers a far different, constructive direction. Think Emerson. Think Nietzsche. Think the better parts of Max Stirner. Think Goethe, Lao Tzu, Jack London, Thomas Paine and Beethoven. Let's not forget Christ and Buddha.
The difference is life ruled by what is best about one's nature, rather than what is worst. What is worst is what is easily corruptible because it is immediate. Ideology attracts people because it universalizes immediate desire. Those who have a higher principle to work toward, a goal by which to always transform and better themselves, are not concerned with who has more power than them.