Sure, its's free*.
- except the cost of materials and gas to drive to the hardware store, which you'll likely do twice or thrice as you realize you bought the wrong thing or need some other specific tool, that you'll use one time a year or less
- except the cost of your own time away from personal projects and family
- except the cost of hiring a plumber afterwards to professionally fix the problem you caused by DIY'ing it without the knowledge and experience that a professional brings
Having fixed several appliances over the years as well as household problems, none of those things get remotely close to the cost and toil of hiring a tradesman. I recently tried to hire a plumber because my hot water heater was throwing an error code and not working. I had to call 3 different people just to wait for the guy to come out 2 days later and quote me over a grand. I fixed it myself instead. The part was $20 and it took 15 minutes.
I see these arguments time and time again, and the two sides fail to see one simple thing: different people enjoy different things. The person who would hire a plumber would pay to not have to do plumbing, the person who'd do it themselves would pay to do it because it's fun for them.
And now you understand each other!
One does not simply "hire a plumber". You're suggesting to find, vet, arrange, brief, supervise, assess and pay a plumber. Your time is still gone and you still pay for materials and gas. Then you still might need to hire yet another plumber to fix it better anyway. If it's really bad you might need to hire a lawyer…