Some more context; they're not only used to interfere with facial recognition. They're also being used to annoy the police officers, as well as people who are watching from their windows when protestors pass by. I've had lasers pointed at me when I was just looking out of my window over the protests.
Depending on the class it's not annoyance but endangers your eyesight. If used (in)appropriately it can definitely be classified as a weapon. A number of people have lost their eye to these things in the past (class 2+) - read on why its forbidden at burning man:
Is there a reason to lase random people looking out the window? Is it to shame you for not joining the protest, or because you could be a police or pro-China observer, etc.?
I'm not sure what the reason is. There's a hotel across the street from me, and some people were looking out of the window, instantly they had 5 lasers pointed at them. Someone was pointing a laser at me too.
Same reason protesters disrupted traffic by blocking roads and holding train doors open during rush hour to prevent people from going to work, disrespect the national flag, etc.
Some of them are protesting for reasonable demands (even universal suffrage is not too unrealistic a demand for Beijing IMO but any dose of separatism is definitely a no-no) but increasingly it looks like the majority are students venting their anger because they found themselves in a bad economic situation and have a long summer break to spare.