How is it possible for Centre and the like to blacklist Ethereum addresses when they themselves are not miners/validators?

Question

There is no shortage of the news on stablecoin censorship, in particular blacklisting of Ethereum addresses:

Tether has been blacklisting Ethereum addresses that hold USDT for a couple of years now—this year alone, Tether has blacklisted 24 addresses that hold a total of $5.51 million USDT in summation. [...] Tether has blacklisted a total of 39 out of the 1.47 million Tether addresses that exist, which represents a total of 0.00002% of all tether addresses. When a tether address is blacklisted, it can’t send, receive, or redeem USDT.

Assuming that the said stablecoin issuers are not miners/validators, how are they able to do censor sending and receiving? Does such censorship involve also NFTs, Eth, and other erc-20 tokens? Could similar censorship be done by MakerDao?

Answer 1

They own the contracts.

For example, one of the Tether contracts is named BlackList. This contains a mapping:

mapping (address => bool) public isBlackListed;

...which can be updated by the owners using addBlackList().

When an address is added to the blacklist, that address can no longer use its Tether balance.