You are assuming that because something can be viewed as 'natural' that it must be accepted as the best option. This is ridiculous on the face of it and ignores our ability to make judgment calls which can and do determine future paths. This is a genetic fallacy which states that because something happens in the past it must be the best option for the future.
Labeling something 'natural' no more makes it appropriate in biological replication/reproduction than it does in medical science. There are many substances labeled 'natural' that are effective medical treatments but there are also some 'natural' substances which are not just poor treatments but can be dangerous treatments. In medicine, the label of 'natural' does not automatically signify something that is 'good'. This is also true of biological reproduction - natural selection is an active and highly effective means of directing the percentage of specific alleles within a population but we do not have to accept the methods used by natural selection as the 'best' thing for a population.
Other animals are subject to natural selection and operate within that limit, for them natural selection is a necessity. That is simply not true of humans. We can evaluate 'natural' processes and compare them with processes born of our understanding and technology and determine the appropriateness of taking nature paths.
We routinely examine processes such as floods and droughts, which by your criterion are quite natural and therefore should be allowed to continue unimpeded, and after making a judgment call as to the appropriateness of interfering with nature, use our technology to prevent, divert or mitigate those processes.
Even if you can make a direct correlation between Nazi eugenics and Darwinian Evolution, we do not need to accept Nazi eugenics, no matter how 'natural' you feel it is, as an acceptable process.
The human mind, and therefore the ability to make judgment calls based on an assessment of past events and future consequences, is very much a part of the natural world. Evolution gave us the ability to recognize and make judgments about the appropriateness of external natural processes.
The removal of inferior members of a population is very much a part of natural selection, but so is communal care of infants and the elderly. Although many anti-evolutionists desire to pigeonhole selection as 'survival of the fittest' with fitness determined by the biggest and strongest and most 'red in tooth and claw' this is nothing more than a false representation of the definition of 'fittest'. In some cases, fittest does mean the most brutal, the most violent, the most uncaring. However in many other cases, fitness is not based on who is the biggest or the strongest or the most violent but is based on those who are the most caring and cooperative. In those cases where the most cooperative are the most fit, those that are most violent are generally a very bad thing for the population - they lower the probability for the population to survive. (I'm not advocating group selection here) In nonhuman populations they will be selected against, reducing the percentage of their particular set of alleles within the population. In human populations we can send them off to war or put them in jails where their opportunity to reproduce is reduced. (Again I'm not saying that the group selects for anything, just that our morals and laws, as well as conflicts between groups frequently result from population demographics and density)
Being 'natural' is not necessary and sufficient to be the best option. Trying to claim that Evolution requires us to mindlessly follow one natural process over another is at best a mistake in understanding and at worst disingenouois.
Eugenics as practiced by the Nazis is not the best path for human populations to take, we have recognized this and have consequently rejected it. That rejection is evolutionarily sensible and just as natural as any other selective path. Accepting evolution does not necessitate we accept the anti-evolutionist concept of 'fitness', just the opposite, our cooperative adaptations tend to convince us to prevent one subgroup from subjugating or eliminating another subgroup.
Nazi eugenics is the antithesis of the most appropriate 'natural selection' as it applies to the current human population.
"do you agree that human are special, not merely just another animal?
As in - special creations of a God? No. We are animals every bit as much as the other apes.
As in - because we of all the animals can document historical events, note their consequences and reconsider similar actions, then yes we are special. No other animal has equivalent ability to make decisions based on historical event and extrapolations into the future. As far as we can tell we are the only animals capable of predicting the consequences of future actions beyond the immediate.
"Eugenics as practiced by the Nazis is not the best path for human populations to take, we have recognized this and have consequently rejected it."
Eugenics as practiced by the Nazis has been rejected on moral, not scientific, grounds.
"It would be wrong to condemn them as bad experiments, if they were carried out on mice."
- Benno Müller-Hill, Professor of Genetics at the University of Cologne, referring to Nazi experimentation upon human subjects (1984).