A direct blast won't negatively effect an already established website much. The argument "If a direct blast is bad, I will just blast my competitor" doesn't hold because you want to take out #1, #2, #3 ... typically whoever is already #1, #2 or #3 is well established enough that an extra blast will only help them.
Then you have your site, which ranks +50 and has no solid standing. It's probably less than 6 months old. You do some quality backlinking and it breaks into the top 10 by the skin of its teeth. That site has a shakey hold on its position. Blasting that with xrumor or scrapebox could easily sandbox the site.
There are a few instances where blasting #1 would cause a google dance and harm your competitor ... that is typically when they don't really deserve to be #1 anyways. And when they don't deserve #1 anyways, its easy enough just to outrank them with proper SEO.
By the time your own site can easily handle a scrapebox, xrumor blast ... you're already going to be top Google results anyways. And then its pretty stupid to rock the boat, even though you might get away with it.