First of all, PPA's are perfectly acceptable as answers here. Sure, it may involve risks, but there's risks of getting malware or at least have vulnerabilities slip through even in official repositories of Ubuntu. So I consider this somewhat of a redundancy to consider PPAs dangerous or forbid them from site.
To me - thinking about quality on this page - it appears to be a problem, when there are answers - especially regarding security critical software - that envolve ppa's.
Tor, first of all, isn't security critical to Ubuntu itself - it is a 3rd party software. It would be different story if this was official Ubuntu package of sorts. Second, tor license is GPL , so they're OK with its distribution, which is what the PPA does.
To quote your original comment that you're referring to:
I'm sure webupd8team updates their packages very consistently and quickly, however I would note that if you install Tor Browser Bundle the way @purbleguy suggests instead, the browser will update itself very soon after an update is available. For someone needing to retain their anonymity, this could be critical. This also removes the need to trust that webupd8team has not made any bad changes to the software (not that they would, but removing trust is always a good idea in this field)
The thing is webupd8 has been around for quite a while, there are numerous software packages there. Removing trust form someone who holds quite decent reputation in the community is kind of . . . don't want to say absurd but that's how it feels. Second, how can you trust tor project itself not to make a baited software, with potential backdoors ?
In conclusion, security sure has always been a trade-off with usability, but it's a trade-off that users should probably make themselves and be conscious about it. I don't mind your comment at all, but requiring every single post on the site to say "disclaimer: PPAs may be bad for your health" is somewhat like listening to those medical commercials - yes we ,know there might be side-effects, yada yada yada - it defeats its own purpose.
So what I am trying to say here, just let the PPAs be.