Others can claim our beliefs are unfounded, but that is their opinion. I have no reason to think my beliefs are unfounded.
The "claim" that religious beliefs are not founded upon substantive evidence is accurately supported by evidence and is therefore not merely an "opinion". Since 'faith' is "a belief without evidence", (as defined by language usage, not by a religion), that's the
reason it's unfounded in rationality/evidence. Of course, it's entirely possible to hold unreasoned beliefs as shown by there being extant religious followers.
Other people can criticize me all they want, but I ignore them. As for the posts from others on this forum, I don't even click on them. If they are in a thread I have participated in, I scroll right on past.
It's probably best for blind-faithers to ignore reasoning and cling to illogic instead; that's an easier dodge than critical thinking/using reasoning.
Remember; others have the same option to oppose religious blind faith as religious adherents do to adhere to it.