The way to lawyers justify their fees

Pretty easily. Lawyers—just like doctors, plumbers, and mechanics—provide a service for matters that most people are incapable of resolving efficiently (or at all) by themselves. I may grumble when my car needs a new part or when I’ve got to pay to get my annual physical, but I lack both the skill and time to handle such issues myself, and therefore rely upon skilled professionals who have spent years performing such work. Nothing in life is free, so while I might not like paying certain fees, they are justified as long as they are linked to the work actually performed and are what I freely agreed to pay.

Lawyers are no different. If you hire me, I am going to spend my time (though no more than necessary) putting my years of experience to work on your behalf to resolve legal issues that you lack the time/skill to handle yourself. My rates are what the market will bear: what I charge right now allows me to remain reasonably busy with paying clients. If I (hopefully) become inundated with work, my time becomes more expensive for future clients, but if I can’t find a sufficient number of paying clients, then my fees would need to drop. It’s simple supply and demand. A lot of people lament the cost of lawyers, but that, too, is a product of the marketplace: all lawyers are trained-professionals who, at minimum, have completed 7 years of post-secondary education and have secured licenses. I think that services like LegalZoom that allow for simple legal tasks to be completed cheaply are a real benefit to consumers, and I have no issue with states allowing certain simple routine tasks to be completed by non-lawyers; people shouldn’t have to spend an arm and a leg to have what amounts to a boilerplate form completed. But complex matters? Even most lawyers aren’t particularly good at that, so those who are are going to be able (and should be able) to charge more.

 Additionally, 

The same way any service professional justifies their fees...

By charging what the service is worth to the recipient in a competitive market. Legal services provide value to the recipient, presumably (else customers would not buy them), and a good lawyer will base his fees rationally on the value delivered versus what other similarly situated lawyers are charging. If they charged higher fees they'd lose customers to the cheaper guys who do equivalent work. Of course, part of the issue is that it's hard to evaluate the value of legal work comparatively, just like car mechanics and dentists--but that's what yelp is for, I guess, and references.

One more thing to note: There are a ton of lawyers out there. People don't like to shop around for lawyers, similar to the way people don't like to shop around for car mechanics or dentists--because it's hard to evaluate skill and value based on short term outcomes. But if they did shop around, they'd quickly find that there's a wide range of lawyers and a wide range of fee structures available. In fact, that's the #1 way that in-house attorneys reduce legal spending: by shopping around and negotiating lower rates.