I presume the question is related to the project sketched in your previous thread **broken link removed**
1. The rectifier "puts harmonics onto the grid" with or without transformer. That's not particularly unsafe but possibly not conforming with regulations.
2. As said, electric circuits directly connected to the grid carry hazardous contact voltage. An isolated high voltage circuit can be however dangerous as well. An important difference is that if the isolated circuit has no other connections to ground or grounded external circuits, touching a single circuit node is not yet dangerous, the operation principle of a safety transformer.