The biggest problem about tether is that Tether is owned by Bitfinex, and Owner refuse to acknowledge this and tried to hide it before!!
I am suspecting that Bitfinex needed money to run due to a huge loss on its previous hacker attack. Maybe they lied and there is actually more than 30% of bitcoin is being stolen, but they could not risk and say the full amount, because this might lead to more problem where consumer losing trust to Bitfinex. So what I believe is that Bitfinex is using tether to finance its situation, and this working scheme continuously print free money and scam people.