It's not on. Particularly if the product is still available for sale. You're cutting out someone's livelihood. It doesn't matter if you don't think the game is worth paying for or not.
If someone was selling turds for £2 on the street and I didn't think it was worth it, it still wouldn't be acceptable if I took one of those turds without paying to test it out before I buy.
And the fact that they're not losing a physical item and that it's just a digital copy means nothing. They're still losing potential revenue.