It's okay even if different researchers are working on similar problems, because replicability is important.
A common control in sociological studies of educational systems is to compare people who are just above a particular cutoff (say a 2.00 GPA), and just below that cutoff (say a 1.99 GPA). These people are often effectively equivalent except for one good or bad day, or one harsh or forgiving instructor.
If an academic department makes 15 positions available for graduate students, it will have 15 graduate students. Regardless. Is the 16th applicant who just didn't make the cut worse than the 15th who did? Probably not. And they might have been better, or at least have been a better fit.
I'm better at science than I am at the replacement job. Ergo the maximum I can contribute to the world is through science.
Regardless of personal intentions, it's also a fact that we have a massive oversupply of people trying to make it in academic science. Functionally the only way it is selfless then is if you are meaningfully better at science than replacement level (and again potential replacements run deep these days).
This makes most people either knowingly selfish (if they are sacrificing others' wellbeing for their research anyway) or very arrogant about their intelligence level. Or naive about the system, but I don't think you'll meet many postdocs that don't know these facts.
The people that stick around and grind away at research work even once any chance at a tenure track position has passed are a lot more defensible as selfless of course, but that's not really the most common situation to find in a lab. The majority are gunning for a career in academic science, even down to the poorly treated pre-PhD RA labor.
Now obviously if some rich kid or someone with no personal attachments wants to fuck around in academia they should totally go for it. I just don't think selfless is the right word for that, and it's certainly not the right word for your typical academic ladder climber.