> Is it really reasonable to assume it's not less safe in this case?

Yes, because this assumption is consistent with the null hypothesis. The negation of this statement is that it is strictly less safe, which is not consistent with the null hypothesis, and for which there is no evidence.

Okay so let me follow. We're fine assuming it's not less safe. So then we must be fine assuming it's not more safe.

These two lead us to your null which is that it is as safe.

When a new unproven technology comes out does it seem correct to automatically assume that it is as safe as the current standard? Would you not expect some proof?

> When a new unproven technology comes out does it seem correct to automatically assume that it is as safe as the current standard? Would you not expect some proof?

In the absence of any data or given priors whatsoever, we should give the three possibilities (less safe, as safe, more safe) equal weight. This means that there is a 33% chance it's less safe, which is too large to ignore. That's why we want more proof when we deploy new tech, introduce a new drug, etc.

But note that specifically in the context of TACC as it stands today, we are not in that situation. There has been plenty of data accumulated already, which constitutes the proof you are looking for (i.e., the data we do have doesn't show a decrease in safety.) That's why today it is reasonable to assume that TACC is not less safe than no TACC.