It's what many have seen happen again and again, and it's what many have experienced themselves.
I understand what you're trying to do here, and you're not wrong. It's rather more about context and how this works in reality.
Your perspective is correct, in that seeing a relapse as a complete failure can actually make it worse. You're right that the best mindset is to get up again, remember that whatever has been accomplished is not lost at all, deal with minor withdrawal, and get back on the horse (or wagon, I guess).
But the perspective of others here is also correct. One of the most common causes of relapse is thinking 'I can handle it now', is moderation, is forgetting the difficulties and struggles of quitting, forgetting the weeks, months or years lost to continuously failed 'moderation', and taking for granted the positive things that happened since quitting.
To someone who is 'clean', it is absolutely disastrous to think that a relapse is not very dangerous. Because the mind wants excuses to indulge again, and even the tiniest thought that this can be possible without potentially a complete reversion to an earlier situation can be enough of an excuse.
But to someone who just relapsed your message is probably very valuable. I think most people here would agree with that.
The thing is, the number of people around who need to hear that a relapse should scare the living crap out of them is almost guaranteed to be much higher than the number of people who need to hear that it's not the end of the world.
Before relapsing, not relapsing is 100% the correct advice. After relapsing, your message might or might not help. I've experienced many situations where no approach helped after a relapse other than, well, waiting and hoping.
And that's why I think people disagree so strongly. Not because you're wrong, but because your statements, in practice, can be harmful to people reading them.