Let us for the sake of clarity define making of a profit as being the trade of that which is given being of lower value than that which is demanded and received.
In general, and not withstanding secondary ethical considerations (such as the consequences of a trade in goods or service not occurring), what would be ethical problems related to trading for profit, and how are they dealt with in philosophy?
Let's say you and I engage in a voluntary trade where you give me A and I give you B in return.
Moral "problem"
A moral problem only arises out of the false assumption that the traded items have some objectively assignable values, like $10 or $20. Then if A has less value assigned to it than B then I lose and you win, and vice versa.
Problem solved: values are subjective and "opposites attract"
The problem vanishes when it is recognized that in a voluntary trade each party values what they receive higher than what they give up. In the above trade, I ranked A higher than B, while simultaneously you ranked B higher than A. We ranked them exactly opposite of each other, which is why we traded in the first place. Every voluntary trade arises out of such opposite rankings by the two sides of the trade.
The "marginal revolution"
Why do different people rank things differently? Part of it is personal preference and taste, but a very important aspect is how many units of something they already possess. The more of something I have, the less subjective value I place on an additional "marginal" unit of that thing. Because people have different amounts of things (goods, money, time, skills, friends, etc.) their rankings differ from each other, which causes them to trade those things amongst each other.
When "Have horse, want cows" met "Have cows, want horse"
Example: I have 20 cows and no horses, you have 5 horses and no cows. We agree to trade one of my horses for two of your cows. Why? Because I subjectively value getting my first two cows higher than keeping my "marginal" fifth horse, while you subjectively value getting your first horse higher than keeping your "marginal" 19th and 20th cows. So we trade and are both subjectively better off than before.
Entrepreneurs and profits
The same reasoning can be applied to entrepreneurs trading things they have (ingenuity, money raising ability, connections, demand forecasting skills, people skills, etc.) to get things that they want (money, prestige, etc.) On the other side of the trade you have customers who trade the things they have (money) for things they want (gadgets/services provided by entrepreneurs). In the trade, the two sides rank things opposite each other, e.g. the entrepreneur ranks $100 higher than the gadget he is selling, while the buyer ranks the gadget higher than the $100 he is spending. A win-win trade is born.
But profits are not forever
If the entrepreneur is making lots of profit, say 50% on each gadget, other entrepreneurs come in to offer competing products, and more competition means more supply which results in falling prices and narrowing profits. So the entrepreneur's initial high profits are a limited time reward for offering something that is so in demand that customers are willing to pay good money for it. The higher the profits, the faster other entrepreneurs jump in and reduce the margins. This is how the market rewards innovation but once innovated drives down prices so that consumers keep getting new things that keep getting cheaper.
I had fun writing this and hope some folks like reading it. Cheers!
Because trading is voluntary, it's always done for profit of both sides. At least at the moment of the trade each of the parties agrees to conduct it. Both sides benefit from the trade. Otherwise one of the sides (or both) wouldn't agree to participate in such a trade because each of them has alternatives to conduct a similar trade with someone else or avoid it at all. It's hard to see any ethical problem with voluntary exchange where each participant profits form it by definition.
Consequently, any forceful intervention in a voluntary exchange causes at least one of the parties less profit or even a loss, or prevents the trade. Therefore, the more relevant question would be about the morality of the such interventions (prohibitions, partial prohibitions by taxation, etc.).
