@mattdm @bontchev You're right, but you're talking with hindsight.
The question is not how you would react with your knowledge right now, the question is did things look weird with the knowledge you had right then and there.

Were the valgrind errors weird? Sure they were.

But there was a responsive upstream, the code was in a "weird" place such as ifunc and compiler optimizations were seemingly involved etc.
The maintainer is responsive, on top of things etc.

The insidious thing is, this is exactly how you need the open source community to react for the whole thing to work.
If we are super suspicious about every contribution, need four people to sign off on every commit etc., would we really have that landscape of amazing open source stuff we have?

I think to assume good intentions is important and should not be given up, even with the experience of being betrayed by a bad actor. Imagine how bad the original maintainer of xz must feel in that situation.

Instead of beating us up over not seeing things that were not obvious, we should approach this better:

Were there clear signs that we missed?

Where there things that gave us a hunch of what was going on? Why did we ignore them?

And on the technical side, I guess we could invest some effort in validating that the tarballs we use to build our source is actually corresponding to the source code we're using.
Fedora already does a lot of things right, e.g. we're not using the shipped configure but we're running aclocal and all the other stuff ourselves.
Improving on that is probably going to get us further than starting to question contributors or contributions. We might not just hit a few backdoor attempts but we might also hit a few accidential maintainer fuckups. And that would be a good benefit for the distro in every case.