I have more of a general aversion to the actions of the (Core) people who support SegWit, including false promises, censorship, and other shenanigans like the 2x trojan horse which we've just seen play out:
https://www.reddit.com/r/btc/duplicates/6iecx7/if_segwit_act...
Can't speak for thefalcon, but implementing Segwit (or any change) as a soft fork creates the possibility of an eventual chain re-org, as well as the possibility for non-upgraded miners to accidentally work on an invalid block. Soft forks have all the difficulties of hard forks (requiring 51% of hashing power to work), with those two additional disadvantages.
I can't speak for the user thefalcon you replied to, but most opposition as I understand it comes from the fact that segregated witness makes things more likely to rely on centralized infrastructure, departing from the original vision of bitcoin as a decentralized system that can't be controlled by entities like governments and banks.