They have already run out of server capacity. They have fewer than 10k users. There will almost certainly be another instance that becomes the default if the reddit exodus occurs as expected.
Also, I haven't seen any instances of lemmy.ml being super aggressive or restrictive. Lemmygrad.ml is blocked by most instances.
If I'm being completely honest, I'll take communists over fascists 10 times out of 10. A leftist backbone is a convenient shield against the alt-right cancer that tends to inhabit these fringe internet communities.