Selling items for a profit ISN'T "wrong" if:
• You bought the item fair and square for a price that was under market value
• Someone contacts you and makes a high offer on a piece you own
• The market price rises on an item after you purchase it
Selling items for a profit IS "wrong" if:
• You lowball or take advantage of someone with the intention to flip whatever it is you are buying
• You misrepresent or lie about the rarity/importance of an item in order to achieve a higher price
• You play potential buyers off against each other in order to get the "best" price for your item
I'm sure you could go on and on about the rights and wrongs of selling for profit but at the end of the day it comes down to treating people with respect.
It's definitely harder not to take the money and run these days and I think if given the chance most people on here would sell an item on for profit if they weren't that attached to it however you still have to conduct yourself properly.
Ultimately greed is the root of all the problems in this hobby, so if you care about your reputation (because we are worse than women for gossiping) and your overall impact on the hobby then do your best to buy and sell in a way that leaves you with a clear conscience.
Collecting should be a fun hobby and not a bunch of people worried about how much money they've made or can make out of others - leave that to the stocks & shares traders!