All distributions make mistakes. It's a complex job. Debian stable had a local root elevation exploit on for a while a couple of months ago and nobody batted an eye. People would have a field day if that happened to Manjaro.
It's a double standard borne out of the resentment of a vocal minority and that sucks. The Linux community wastes so much energy on these pointless feuds. (And then they wonder why there's never the year of the Linux desktop...) Linux and FOSS are not about treating user share as a zero sum game but unfortunately there are people who can only think in terms of "if you use another distro you're dumb and I must ridicule you".
It's an especially narrow-minded take with distros like Manjaro, which is different enough from Arch that its users were never going to use Arch anyway.
How long have you been using each of them? In my years-long experience it's been the exact opposite. Manjaro goes out of its way to not break anything and offers safety measures out of the box to recover if something should break. Arch doesn't care, it introduces breaking changes all the time and expects its users to be able to cope with them.
They target very different types of users and have very different goals. Manjaro explicitly tries to be stable and user-friendly whereas Arch exclusively caters to advanced users and aims to be customizable above all.
You can achieve the same with Arch that you get out of the box with Manjaro but it's not there by default – because that's not something a lot of Arch users are seeking.
What's a "normal" user? On Linux you get all sorts. But you will most definitely notice a difference between daily driving Manjaro vs driving Arch.