No one at any point said or suggested that legal trade should equal smuggling.
Legal trade without missions nets you nearly nothing or negative after factoring in fuel/supplies/crew pay. That is not a reasonable state. Smuggling can double costs, Legal gets you nearly nothing. A 10-20% return on legal trade costs would make it viable.
It's not selfishness, it's you objecting to something no one said.
My point
is that peacetime legal trade between core worlds lending you a 2-3% profit margin at best is a perfectly reasonable state of affair. Again, there is zero risk involved in it. You can know in advance where the pirates are by reading your intels, pathers can be bribed and even without that it's not hard to make a trade fleet either impossible to catch up to or strong enough that the odd pirates or pathers wont want to go anywhere near it. If you are engaged in battle while trading in the core worlds in peacetime you're doing something wrong.
You already get the 10-20% profit margin on legal trade by trading on shortages, but that often involve risking your fleet in systems that are raided by pirates so at that point it become reasonable.
Profitable open market trade makes no sense, both gameplay wise and in setting. Not a 20% profit margin anyway. A 30% blanket tariff on everything isn't there by accident. It means the factions don't want you being involved in trading their stuff. Each probably already has their own chartered trade companies/merchant guilds/subsidiaries handling the trade for them and they don't want the competition from you and your rag-tag fleet of Hounds. Now, maybe there could be a more involved way to do legal trade than just pressing F1 on your cargo and checking your intels from time to time, maybe you could become one of those company that trade on behalf of a faction and maybe having a comission could grant you a lower tariff or a tariff-free quota in the ports where you're comissioned.
Making legal trade more interesting with new features would be welcome, sure. Just making it more profitable by fiddling with the numbers until you get a profit margin that seems reasonable to you is the lazy way out and would potentialy ruin the smuggler gameplay by making it irrelevant.