How is it free? You had to do work to get the materials or marks. You are spending your resources on something. If someone wants to spend their marks to buy reputation instead of guns, armor, or materials, how is that choice wrong? I can see an issue if there were no caps on how many marks we can have, but we have caps on how many we can get each week and how many we can have total. As it is the time you spend to gain 100 marks you would already have gained more reputation compared to what you can buy.