Should legendaries be let in gyms?

Yes

IMO yes.

One per gym limit (nobody wants to fight a gym with 6 legendaries stacked up), and maybe holders of a gold gym badge only (to make the gold gym badges a more meaningful reward - not because I think it matters for balance).

Articuno and Suicune were made for defense, as are some of the upcoming legendaries in gen3. And I want to get to attack normal strength versions of the legendaries.

Oh - you know what would be cool? Making it so that you can't attack a gym with the legendary that's in there - in the spirit of the original games having legendaries be unique.

mew2 gonna kick a$$

Raikou makes a great defender. So does Lugia. Suicune has potential as well (if it has Ice Beam).
And don't forget Confusion Mewtwo

I don't mind having a gym full of Legendary's, given the way gym defenders lose Motivation. They would be tough, but not significantly tougher than Blissey - players below Level 30 might have trouble, particularly if they haven't optimized their Mon's to take down Legendary's. But if they've built up their Mons to be helpful in Legendary Raids, they'll have a team that can take down a "normal" Legendary. (ie: Not a raid boss. A Level 40 Tyranitar in a gym isn't too hard to take down if you've got a few decent Machamps, but one person isn't going to take down a Tyranitar as a Raid Boss for example)

It's not too much to expect a majority of players will be able to deal with any Legendary that's placed as a gym defender, so I don't see why it should be limited to 1 Legendary per gym on that basis.

Still, 1 Legendary per gym is better than 0 Legendary's per gym. I'll take 1 over 0 any day, even if I'd really like it to be 6 per gym.

I would LOVE to drop my level 30 Articuno in a gym. Any of my powered up legendaries, really to show them off. I'd be more likely to Golden Razz them from time to time to keep them looking all fancy! This would then cause me to raid more to get more legendaries and more golden razz. Come on Niantic! You can make money off of this!

Yes, even though I don't have any legendary I would still be happy to see them in gyms. Golden berry is the best gym defender anyway, so I don't think legendaries would be "too powerful". Bring 'em on!

I think one legendary per player would work even better.
Every player could be allowed to put one of his legendarys into a gym.
If he has the goldbadge of that gym and there is no legendary already.
That wouldn't initiate a rush and let a lot more people show of if they want to.

But, well, still a lot of people think that legendarys are legendary because of their strength and power in battle.
Wouldn't it be bad for their reputation if you expose them to actual gymfights?

Sure. I'd rather deal with 6 legendaries than 1 blissey.

Yes!

Why would you put a legendary or any good defensive pokemon into the gym? I have pidgeys locked in a gyms for days and weeks... in a current gym system any defender is useless.

I would be on board only if there was a limit of one legendary per gym

I also agree but don’t think unfair is the right word here. It is a fair policy, but a dumb one.

Yes...with only the same limitations every other mon has.
One of each only.

A gym full of legendaries would be...well...legendary!

I would stop to take on that gym any time I saw one - and people that missed out on the raids can at least get the shadow in their dex.