Because data collection that is "sufficiently anonymous" _does_ respect privacy. If it's completely impossible to tie the data collected to any one particular user, how does the existence of that data compromise privacy in any way?
We can go into an amazing yet pointless semantical argument of what "privacy" means. But let's look at this from a different perspective:
I like your faith. However, if this change goes in, and the capability is there, it will get misused. Because, statistically that's how these things go on this planet+capitalism.
Actually, the way they're implementing this, even if Mozilla decided to try to misuse the data in the future, they still wouldn't be able to, since the data itself is "sufficiently anonymous" (unless of course you want to argue otherwise, like the root comment was suggesting you do).
Or are you saying you're worried that they could _start_ collecting non-anonymized data in the future? If so, I don't really get that argument either. People always have the ability to change what they're going to do in the future, Mozilla deciding now not to collect this data wouldn't change that.
Remove all "we respect privacy" from the advertisement.
It's misleading.