In italian the zz in pizza is voiced loud, in razzo is unvoiced like in the example you made. And of course I assume that pizza is na italian world, and all english dialects that pronounce different from the original are wrong
It's pretty hard to pin this down firmly since attested pronunciations range wider than you seem to think, but based on what you've said in this thread, it seems like a good idea to sanity-check on the voiced/unvoiced distinction.
Well, we have also razza and razza (as in race/breed and spoke/ray/stingray) and they are respectively /ˈrat.t͡sa/ and /ˈrad.d͡za/ where the difference in pronounciation is key to the meaning.
Pizza is definitely /ˈpit.t͡sa/ (and both the t and the s are voiced).
Razzo (rocket) is /ˈrad.d͡zo/, BUT razzolare is /rat.t͡soˈla.re/ .
The z, single or double, is one of the tricky ones to pronounce properly, in Italian they are usually called zeta dura and zeta dolce "hard z" and "sweet z".
Things like this is why using example words to clarify pronunciation is often a bad idea, especially with a language as diverse as English.