One of the downsides is your job can be easily outsourced to a country with lower wages, and with remote work here to stay (IMO), that is going to be even easier than before.
There are no remote plumbers.
I firmly believe that if you show up on time, are pleasant, and are competent at your work, running your own business is a slam dunk and you can charge whatever you want (within reason). Because my experience is that it's nearly impossible anymore to get all of those things.