And if it would bring down steem to 1$ as well, it would be a big hit in terms of growth
There is no basis for expecting that, I don't even know where that number came from. Prices may always fluctuate for a variety of reasons but the most direct short term effect on STEEM from STEEM to SBD conversion is positive for STEEM because people would (under the right conditions) buy STEEM to convert in to SBD.
And thereby also burn the STEEM, reducing supply and likely contributing to even greater upward pressure on prices.
Exactly!