I guess what upsets me about this is not so much the raid, but the inhumanity in how it was carried out.
I understand what your saying, but what's the solution? (Not downing you, but honestly asking) It's going to see inhumane any time they are taken away from their families, and the probability of getting caught is going to be higher at busy, public places like that. Festivals are usually held around the holidays. Officials can't treat holidays as "free" days when they know they're going to be there, especially with the legal citizens growing increasingly upset. What about birthdays, if they arrest parents on a kid's birthday is that inhumane too?
I don't think there is a "good" time for this to happen. Although if it's crowded like that, I think they should have a better way of handling the panic. It would have been better if they had a central enter/exit point people had to pass through and they could just single them out as they were exiting.