I'm curious to know more. But I also think it's important not to paint all meditation with the same brush. Transcendental Meditation® is it's own weird thing.
Meditation and yoga have taken the ‘Western’ world by storm. This is because they are extremely easy to instruct. Close your eyes, breathe evenly, etc.
Those who know (yah pasyati, sah pasyayi - are initiated in scripture and are able to ‘see’) understand that meditation is the end portion of a spiritual path, the last stage before enlightenment.
Every single canonical text mentioning meditation mentions how essential it is to control the mind first, before meditation. Yet most people end up using it as a way to calm down which is not the intended use. It is unsurprising that they end up hurting themselves. Most can’t continue the practise long enough to do that anyways because for a beginner your mind will be jumping within 5 seconds or less.
It doesn’t matter much anyways. Most people are not Really meditating when they attempt to do so, more just relaxing.
Source: Scholar of important ancient Indian texts.
I can't speak for the author of that comment, but here's my take:
When you meditate, you're creating in essence an open space in your mind. (A head space, if you will. I will not, because that's pretentious. But feel free.)
That empty space is an invitation to anything out there that wants to fill it. If you're spiritually minded, you might think of it as an invitation to spirits to come and fill your head with new ideas, and wouldn't you know it, evil spirits love that sort of thing.
If you're secular/rational/scientifically minded, just know that if you calm your mind, you WILL get other thoughts replacing the ones you just calmed down. If you sit down feeling guilty, your meditation will likely be dominated by thoughts of guilt. If you're angry, you'll likely obsess about that anger.
The usual advice I've been given is to let it happen. Let those "evil" thoughts come, take note of them, and then let it go. If they come back (and they always come back), note them again, let them go again.
The danger is if we get attached to these ideas. Then they grow and become the basis for depression or anxiety or any number of other ailments.
The opportunity is to be able to see that these thoughts and feelings aren't any more real than anything else; that we don't have to act on them; we don't have to identify with them; we don't have to let them control or even influence how we really feel, think, and act. They're just passing thoughts. We don't have to hop in their car and go for their ride. We can keep walking.
It's probably because they directly conflated their experience with TM with meditation in general. Many people in the meditation community have strong views on TM in particular, in my experience.