Thanks for the free promotion, they would say.

"Tether is a fully transparent company"
No it isn't. They publish their reserves on their website, is that 'proof'? Their audits are always partial and I haven't seen them audited by an external impartial auditor. You'll have to trust them.

"Once someone exchanges Tether currencies into fiat currencies, the Tether currency will be destroyed"
Then why is the circulating supply of tether only ever increasing?