Why does Mars rejoice in the 6th House/ is a good placement for the planet ?
Mars in the 6th House
That's because malefic houses such as the 6th house enjoy the rougher handling of planets like Saturn or Mars.
The 6th house represents the conflict we encounter in the physical world. The 6th house happens right after the 5th house, where everybody expresses themselves freely. What emerges as the result of this is the clash of egos, because people's ideas and identities are bound to come into conflict sooner or later, since the ego always seeks security through coming out on top. One person's freedom of expression is limited by the freedom of another, so someone always feels the discomfort of their space being taken, and that leads to conflict. That conflict happens in the 6th house.
The conflict in the 6th house never stops, because the 6th house is 12th from the 7th house of mirroring. Go to my masterpost and read the post about the 7th house to find out more about this process. The 7th house is the place of the death of the ego, because as a result of all the 6th house fighting in the 7th house we start seeing how other people's actions and feelings mirror our own. We shed ego illusions and we face who we have become through how we relate to others. Then in the 8th house, together with another we decide on a mutual agreement, that should be beneficial for both parties by going to the bottom of any given problem.
However, any house 12th from itself leads to energetic losses in an area of that house. So any person with 6th house placements struggles to go past their ego and see the truth through another as the 7th house would, as they are focused on fiercely defending their position. So instead of surrendering their ego, which the 7th house requires, with a 6th house planet they fiercely defend it, because the person here feels constantly challenged by other people's ideas or presence.
The 6th house thrives on conflict and confrontation. That makes it a tough place, but sometimes a necessary one. There is a time and occasion for everything. Some people in some situations need boundless compassion to heal, but some people need tough love for their own good, and that same compassion given to them would enable them and prevent them from growing. The 6th house is imperative in defending our boundaries, which ultimately helps everyone involved, because when you let people step over you no one really wins. They don't really win, as their spiritual growth suffers from being enabled by you, you don't win because you didn't love yourself enough to give yourself the protection you deserve. I have zero 6th house planets, and a 12th house Jupiter so I'm endlessly giving by nature, but years of living with my roomate with a 6th house stellium have shown me the value of the skill of putting people back in their place. It really is a loving thing to do sometimes.
That is where Mars comes in handy. In the 6th house, Mars has the power to beat obstacles that arrive on its path, and uses them as fuel to advance its position forward and feel driven towards accomplishing its goal. Mars likes being here, because it has a very clear task, an outline, a line of direction, like a soldier receiving a clear command to target a very particular group in the enemy army. There is a fierce precision to Mars being here, which gives Mars a high level of fulfillment.
Whenever life presents you with situations, where you need to defend yourself, you will have the drive and energy to make sure no one walks over you. That is a very useful ability, that you should use for good, to perhaps advocate for those, who can't take care of themselves. As someone who largely struggled with that skill earlier in life due to debilitated Mars, I can tell you from experience how good it is to have that trait naturally. Just be careful to use that energy productively instead of actively seeking out conflict.
