I'll answer your question with an equally valid one, "What proof do you have that once vaccinated you CAN'T still spread it?"

We have never had a SARS Coronavirus pandemic before. We know a lot more than we did a year ago, but vaccines have only been around for about 6 months. Comparing it to other vaccinations may seem logical, but is mostly irrelevant from a factual point-of-view.

So far the anecdotal evidence seems to suggest that being vaccinated helps prevent any transmission, too. However, with all the new variants out there the medical community is suggesting that there is no harm in being cautious until they can be more sure. Also, referring to others as "sheep" and their opinions as "B/S" is totally unhelpful. Let's all at least try to be civil with each other.