It's not either/or, black and white. Those people who compete to do speedruns they have already played through the game once and usually several times, otherwise they could not know how to optimize the speedrun. Thus saying it 'destroys' their gaming experience is a redundant argument, really.
They can both enjoy the game as most do, and afterwards have fun competing/optimizing the speedrun. Fair enough that not all see the appeal in that (it's about competition, knowing a game's structure intimately and min/maxing), but the default dismissive/derogatory comment that many seem to have against this practice is uncalled for. It's almost like your enjoyment of a game, or way you play it, is threatened by speed-runs?
If not, and you don't see the appeal, then just ignore it?
I don't do speedruns myself, but I do see the appeal (after having enjoyed a game the 'usual' way first of course) and from a gamedesigner standpoint it's also interesting to see how the game system can be 'gamed'. The best speedrun I've ever seen was the Morrowind one, I almost laughed with glee the entire way, it was so fast and extreme how a giant game was bypassed that way, and the poor final boss didn't even finish his speech before he was dead
Good fun! Especially because there was no cheating or exploiting of a bug done, it was all made just doing what the game was intended to accomodate. In my view it says a lot about huge RPG's games where this is possible without cheating, they are true sandboxes, complex games that can be gone through in many ways. And I see that as positive.
Well, many words, hopefully it can nuance views about speedrunnings a little. Felt obliged to write it after seeing all the opposite (automatic and oft-uttered I suspect) opinions
Edit:
Here's the Morrowind speedrun I was thinking of:
https://www.youtube.com/watch?v=m1IRxTN-_kU
It's been done 4 minutes faster than this, but that's by using glitches/exploits. This is done 'cleanly', it seems. And there's been a lot of competition over this. You might not see the point, and that's fair of course, but I kinda' like watching such things (after having completed the game in question myself first)