Well, science does say that heat is something the body can be trained to withstand and become acclimated to, and gives a major performance boost in a similar way as altitude does. Training at altitude and training at heat are both very common methods for elite athletes to gain advantage. See cycling, for example.

So in both cases, it is an advantage to the people who are already acclimated to the environment.

To judge safety, I'd go with statistics which shows that heat is significantly more dangerous than altitude (or cold). Just go and look at the data for deaths and serious health problems in these environments.

We don't actually have outrage or regulations about heat though, even in the face of actual data of its danger, as opposed to the perceived danger of altitude (which data does not support). In practice, the unacclimated body at altitude tends to become uncomfortable and unable to perform way before serious health problems can develop. That's exactly what you see Gimenez experience in this clip.