For what it's worth, I think that both the parent and the grandparent are valid opinions.

One says that open source projects should clearly state when they are not meant as a serious replacement for standard tools. The other says that they disagree and that open source projects don't have to give any warning.

I guess I am a little in-between: if you open source your code, I don't think you have anything to do (it's already nice to put an open source license on it). If you advertise your open source tool (e.g. on this website), then it is polite to set expectations.