OK, so the chassam sofer says that. So what?
Nobody is arguing that your practice (and my practice, as it happens) of not doing metzitza b’peh is illegitimate. We’re just saying that other people’s practice of doing metzitza b’peh is legitimate.
There are other opinions besides the chassam sofer. You can’t say an opinion is illegitimate because of the chassam sofer.
I trust that their rabbonim are acting in good faith, and are basing their decisions on the torah. And that’s enough for me.