“There’s a house for sale I’m interested in buying. Is it illegal or unethical for me to approach the seller and find out what price they’ll take?”
It’s not illegal. And it’s not literally unethical because you don’t have a formal code of ethics to adhere to like Realtors do.
Better words to use are “improper” or “inappropriate”. Or perhaps even “self-defeating.”
The seller hired their agent to represent them in the sale and negotiations. They don’t want to deal directly with homebuyers.
Your actions would give the impression that you’re pushy and aggressive.
Escrows are complex business transactions that require good faith and working together. If the seller and agent think (rightly or wrongly) that you’re a jerk, they won’t want to deal with you in a 45-day escrow.
Bottom line: go through the agents.