> I'm not selling them at a loss, if I can't get what I paid for them it means they are by definition worth less.
You have taken a loss. No one who holds the stock is taking a loss. That's why gains and losses can be "realized" and "unrealized."
> Because I do not want them anymore it mean that that market has one less buyer so demand decreases by at least one.
The demand curve shifts to the left, and since stock buyers and sellers are the same people, the supply curve shifts to the right, and, yes, the equilibrium price drops. (edit: Come to thnk of it, the supply curve doesn't change, since it only reflects shareholders and you're dropping out by design. Still, the price goes down.)
But... the company still has all the same employees, still has the same hard assets (real estate, machinery, etc) and is still earning money. The company's fundamentals remain unchanged by a boycott of its stock.
The dividends they pay out per share remain the same, since those are dictated by profits and those haven't changed.
Their investors' assets are worth slightly less, but those investors are the ones who bought your shares, so they actually get more dividends paid out to them.
You've thus managed to reward the people who held on to their stock by making it cheaper for them to acquire more shares.