It's never unethical to ask for more money
In all transactions, any amount both the seller and buyer agree to is a morally sound amount. When you sell something, the amount doesn't have to be fair to the buyer. They'll be the judge of that. It has to be fair to you.
Ethics are useful when selling gauges to the injured but absolutely useless when selling Linux Administration Services to Your Employer. Your Employer is in the business of Making Money. Happily this is the same business you're in, you just go about it a different way. You're asking your employer (or client, same thing, you're providing a Valued Service) to share a bit of the profit they make because of Your Services. Nothing wrong with that.
Next time you feel guilty about a number, remember that it's their job to decide it's fair, and yours to decide if it's something they're willing to go for.
How do you counter for a better salary?
Easy. Instead of agreeing to a small number, ask for a bigger number.
Your client has a Need and you have a Solution. The client values the solution at 100 Galactic Credits, but will start at 6030 Galactic Credits because this is something you might agree to. When this happens, you will counter with a greater number (8060? 80? 90? Do your research!) because this is something they might agree to. I won't go into negotiation tactics here because a) it's off topic and b) there are better resources available (more on that later).
You do not have to justify your price to anyone. This is extremely uncomfortable if you've been brought up with a mindset that promotes fairness, which is a concept designed to limit the number of loan-sharks in a given community.
That particular decision path in your brain misfires whenever you're faced with a negotiation, and that's what's causing you trouble.
Further Reading
- Salary Negotiation: Make More Money, Be More Valued
- Kalzumeus Podcast Episode 12: Salary Negotiation with Josh Doody
- Ramit Sethi (look him up, read his stuff, watch his videos)