Although Regulus only made the protagonist job harder later (this is the horocrux that kreacher has and isn't where 'it's supposed to be'), he at least was the one to suffer in that trap instead of ordering his slave to drink it (it was the one in the lake of inferi where the only way to access the horocrux was drinking the pain potion).

Truth to tell, i think he was kind of suicidal.

Anyway, the books are full of stupid plotholes, I think this was intended as a actual redemption (Dumbledore drinks the same potion later while trying to find the horocrux).

It's just that Rowling can't write something like this without it being laughable - for instance, they find the thing because before dying Regulus took the time to write a message to put in the container where the locket was with 'R.B. was here' (Regulus Black).

And that's moronic.