[awm]

If you play that 2♦ is not 100% game forcing, there are pretty big advantages to playing 3♥ as natural and forcing. While a 2♥ call would of course be forcing, the issue is auctions like:

1♠-2♦-2♥-3♦-3♥
1♠-2♦-2♥-2NT-3♥

Suppose that the two-over-one bidder's second bid was not forcing. Is opener's 3♥ here forcing (choice of games) or just a weak 5-5 or 6-5 majors hand? Given that people do open a lot of really light hands holding great length in the majors, it seems like it's fairly frequent that opener will have a non-gamegoing 5-5 or 6-5 (probably more likely than a game forcing one). Then again, how would you bid the game-forcing majors hand if this was NF? Playing a direct 3♥ as the big 5-5 hand solves this problem... and the loss of the splinter is not that big a loss, especially if a direct raise to 3♦ would be forcing (which it should be).

Of course, if you play 2/1 is 100% game force, there are some issues with "how big a hand does opener have" because people don't seem to ever show/deny extras in 2/1... but at least both the above auctions are forcing, which makes the splinter treatment more appealing.