It is not unethical. Everybody gets to bid.
If you're ready to bid more than you have, but don't want to snipe - just make a higher bid in the first place. The sniper might not win the item.
Example:
The opening bid is 1 dollar
You bid 2 dollars (therefore it remains at 1 dollar)
Nobody bids
A sniper bids three dollars. He wins it at 2 dollars.
If your bid would've been at 20 dollars, the sniper would've lost, because his bid was at 3 dollars.
There was some site explaining why snipers are awesome, but I don't remember the link.