@ Corr - I personally tend to avoid most Alpha / Beta's my self for the pure reason that I love playing the "finished" launch product and don't want to ruin the final gameplay experience
In the case of games like Destiny where I was really unsure if it was a product I wanted to play, I jumped at the opportunity to try the Alpha as it gave me a decent overview of a game that I might have not considered due to its MMO-esque format... but it's single player aspect just won me over!
But Yeah, BETA's are, for obvious reasons, hideously buggy at times and can ruin the entire experience for me.