There's more than a little difference between Google and Canonical. Though,
that said, fiduciary duty, which is the legal requirement that all officers
of a company/Corporation act at all times in the organisation's best
interests (meaning best economic interests) stands contrary to the idea of
community, sharing, freedom and openness.
If one could claim, with certainty, that every single line of Trisquel had
been audited and was guaranteed to be not just 100% libre but also 100% safe
(perhaps such a claim can be made and it's just that I don't know about it)
then one could safely say "Trisquel is guaranteed safe despite being based on
Ubuntu".
Having said that there perhaps needs to be an acknowledgement that, by
reputation, Canonical take a lot of Debian and add their own stuff so they
rely on the Debian sources being kosher, which is more likely than if
Canonical wrote the entire OS from scratch.
So no, there is absolutely no comparison based on what is currently known, to
liken my argument to that of the prism break site. Google are known to be
evil. Any dalliance with them is a dance with the devil. Canonical are caught
on the horns of a dilemma - torn between having been born in the Open Source
community, but trying to find a way to monetise it without charging for the
OS or ending up trying to peddle an advert ridden monster that no one would
want.
No code can be trusted that you can't verify yourself and if you lack the
knowledge to verify it yourself you either learn or choose someone else to
trust, which just comes down to listening to arguments and observing to see
what fruit each view produces.