A lot of the hate stems from either a fundamental misunderstanding of how segwit works (or misrepresentation of how it works) or from hatred towards the Bitcoin Core developers.

Segwit does multiple things. It essentially defines a new type of address which, when spent from, does not have its signatures in the txid calculation. It also redefines the block size limit as a thing called block weight. A lot of opposition is from this block weight re-definition. The block weight makes spending from segwit addresses cheaper (less block weight) than non-segwit addresses, and a lot of people did not like that for some reason. This re-definition also means that if more segwit addresses are being spent from, then transactions will take up less block weight and thus more transactions can fit in a block.

Segwit allows for second layer solutions like the Lightning network to exist more easily. The Lightning Network is what would allow for atomic swaps, not segwit itself.