The purpose of having people on ignore is so they can't harass you. If you comment on someone else's thread, then that member you have on ignore can comment on your replies. This can allow people to harass you, and yes, it happens. If someone starts a thread, they should be able to continue their self care by not having the people on their ignore list able to respond to them. If someone starts a party thread that you can't comment on, then start your own party thread.

People shouldn't be forced to interact with those they don't want to, for whatever reason.

If a moderator wants to start a new thread, then let them, but someone's thread shouldn't be hijacked because they are being safe and practicing self care.