Is blood donation harmful to a person's health?

It can be. I have had to temporarily suspend blood donation. I used to donate blood plasma once a month, but it drained my body of iron and I developed an acute iron deficiency. I had to have an iron infusion and a colonoscopy, a gastroscopy, and a pill endoscopy to investigate the iron deficiency. I now take iron pills regularly.

However some people have donated blood plasma hundreds of times, and it doesn't affect their iron levels. 

Blood donation is safe for healthy adults. There's no risk of contracting disease. New, sterile equipment is used for each donor. Some people may feel nauseous, lightheaded, or dizzy after donating blood.

If your going to donate at least get paid and donate plasma. My first time donating blood 26 years ago. They did a number on my elbow vein and left a 2 1/2" painful bruise on my arm that lasted about 2 weeks. Not even an apology.

Never donated blood ever after that either and never will.

No. The only issue that could come about is over donating which could cause anemia. That is why there is a limit to how often one can donate and a minimum time between donations. Also why blood iron level is checked before on can donate.

No not at all 

It helps people's health 

No when i was overseas with the Military we used to give blood 4 times a year

no, if anything it is a net positive