Surely Elrond would have insisted on Merry and Pippin NOT going?
 

As the membership of the Fellowship was being decided, Frodo, Sam, Gandalf, Aragorn, Boromir, Legolas and Gimli were clear choices. But surely with the entire future of Middle-Earth at stake, Elrond would have insisted on Merry and Pippin NOT going. Glorfindel and one other of Elrond's household were clearly better options.

But he didn't.

Gandalf had a 'gut' feeling that Merry and Pippin needed to be part of the Fellowship, and communicated that to Elrond. The latter apparently trusted Gandalf enough to allow the hobbits to go along.

At the risk of being pedantic, why 'surely'? If it's not what happens in the book, it's not what happens.

Elrond did express his misgivings of course, especially about Pippin: "My heart is against his going." And of course he also had the wisdom to see that there would be trouble in the Shire, but for all we know without the experience they gained in their further travels Merry and Pippin might not have been that useful in resisting Saruman anyway.

On a side note, this scene has what I would consider a very piercing example of Professor Tolkien's generally overlooked subtlety, just after Pippin's made the "send me home tied in a sack," joke.

'Let it be so then. You shall go,' said Elrond, and he sighed. 'Now the tale of Nine is filled. In seven days the Company must depart.'

Consider how much is conveyed in so few words.

Personally I do think it's a bit odd that Glorfindel doesn't do much after rescuing Frodo and co in Eriador. But given that Professor Tolkien considered including him in the Fellowship but later changed his mind (see the Histories) he probably just wasn't considered to be a character who could contribute that much to the narrative.

While I'm by no means an HOME scholar, I recall Tolkien had earlier drafts of what became LOTR as being much more hobbit-centric. For example, the Strider character originally being a hobbit, and gthe overall tone of the first parts being much more lighthearted and closer to The Hobbit. The story changed, Strider becoming a Man and adopting a more ominous feel, but I wonder if Merry and Pippin couldn't at least partly have been a compensation for that, and a means for Tolkien, who admittedly had a great fondness for scenes involving hobbits, to justify writing a few more of them.