Thats because fencing swords weren't as strong as broad swords all this depends on the type of sword, era of time, and type of style in fighting. And Amour.
You got a good point there. I missed that keyword, fencing.
In dervish style combat, and many martial art style, you gain a lot of momentum from the movement, without the hugue disadvantage of a charge. Many fighting styles actually had "sword dances" litteraly (some of which are still danced today) because those cute movements are not just for show. In the western world, the dervish were known to be verry deadly.
There is much more in combat than hiding behind layers of armors and using an expensive weapon.
But there is no doubt in my mind that the plate is great for specific usage (guard, bodyguard)
and very poor underwater 
Dervish-style combat? Momentum from movement? Huge disadvantage from charge?
You've contradicted yourself multiple times in the course of one sentence. Any momentum from spinning around like an asshat imitation of Drizzt Do'Urden is going to be far inferior to that gained from a charge. Even D&D acknowledges this, by the way, so pull your head out of that fantasy *******.
FYI, those 'cute movements' ARE for show. They look lots nicer to the untrained eye than the functional movements of a real martial art.
Armors is overrated. It only protect from unseen openents or stray arrow. It also have negative effects on manoeuvrability. Usually really heavy armors were meant for kings that never needed to fight. They were surrounded by elite bodyguards that did the real fighting. In medieval time the typical armor would be chainmail
What Beechy said.
I'm an engineer. You however don't seem to have a clue what you're talking about.
Look in a mirror. Also, please tell me where you went to university.
1. late medieval / early renaissance had light steel - a hugue advance in metalurgy
this made plate practival for gurds and bodyguards.
the plate had two advantage for thoses jobs
the guards would survive long enought to raise the alarm (indeed you can't slash his throat)
the guards could use themselves as body shields to protect their lieges (nothing better than a ring of plate guards)
Epic common sense fail, history fail, martial arts fail, and intelligence fail.
Plate armour was used because it did its job very well, and with minimal drawbacks. The weight was generally quite acceptable and very well distributed (compare to modern infantryman).
3. the best way to take down a plate wearer is a loaded gun or a loaded crossbow at point blank
Uh-uh. The Royal Armouries has a small article on bullet-proof plate, go read the damn thing. It doesn't help that you're suggesting that the theoretical engagement take place at POINT-BLANK range. That rarely happens, because nobody is going to be foolish enough to attempt to cock or reload either of those weapons in the midst of a melee unless there's some very special circumstances. Ranged weapons are there for a reason, they're there to fling pointy death at your enemies from RANGE.
Also, try holding your ground and aiming carefully when the ground is positively shaking and there's a full line of faceless, armoured men on warhorses thundering down on you. It'll change your perspective a bit.
4. you won't change histoy, plate was never widely used, always restricted to some positions
don't get fooled by medieval games, they're not as reliable as archeology/history books
I believe that you are the one trying to 'change history' here. It was used by almost everybody who could afford it. Even common men-at-arms had bits and pieces of plate, usually helmets and the like.
5. the main purpose of armor is disusion, you know as peasants you would take heavy losses
and prior to firearms, fighting required at least a decade of training
peasants were no match - but bandits might
No...just no.
Fighting required at least a decade of training? This isn't some fucked-up wuxia show where you have to spend a decade in quiet contemplation to learn the 'Immortal Thousand Palm Technique of Invulnerable Asspwnage'. It doesn't take long to pick up the basics, and you'll generally learn pretty quickly when your life is on the line. If you don't, you'll usually be too dead to care.
1. find two high end athlete of equal performance, buy a plate to one of them
2. organise olympics game (sprint, run, distance run, high jump, long jump) and see the results on various weather
*and keep in mid modern "medieval armors" are about 100x better than the real thing, being made today*
*they lighter, stronger, more flexible*
in the real world, a plate would have been a problem on most real world terrain
-swamps, muddy ground, high grass, forest, river bank, sand -
a plate is a big disadvantage in those environment
I call strawman. Sticking any amount of weight on an athlete will impair his/her performance, no matter what kind of weight it is. Give the average sprinter a pair of weighted shoes and look at his/her performance plummet like a stone.
Also, using specific instances where encumbrance sucks isn't helping your case. Even in those cases, plate armour is far less encumbering than you'd think. I'd rather have a suit of plate armour on me that's of equal weight to modern infantry equipment than the infantry stuff itself.
to guard the entrance of a castle from behind wall on a stone floor, where all corridor are tight so you can't be flanked, the plate is the ultimate thing. this is what it was desined for in late medieval era, and it kept being used that way through the renaissance
Wow, really. They only ever had one-way corridors in castles, without ANY side passages?
but anywhere before the 13th century, you would see it on kings and queens (need I say either too old or too young to fight most of the time) well surrounded by eliite bodyguard.
Shit...plate armour was around before then? What, you channeling Dimos or something?
wearing a chainmail instead of a plate give you a tremendous advantage, you got to be verry unimaginative to think the plate wearer isn't going to loose his footing, even inside a castle, when faced by a highly mobile chain wearer
I call epic bullshit. Mail is even more encumbering than plate. Given an equal weight of mail and plate, the guy who's wearing the plate is going to be far more mobile. Also, between equal weights of both, the plate is going to provide more protection than the mail.
actually do I need to say he'll be swarmed by chaimail wearer, simply because they move faster. Those thight medieval castles corridors were all built to prevent swarming.
Refer to above. They do not 'move faster' because mail is a bitch (comparatively) to move around in. It hangs and generally places weight in awkward places, as opposed to a suit of plate.
I can't recall anyone dancing in plate. You can definitively dance in chainmail. Do the maths. Dancing is a good measure of a unit manoeuvrability and ability to sychnronize with other inits or react to unexpected situation. It also determine who can catch who. who can escape who, and who's swarming who. Basically the ability of your soldier to dance in their armor is a good measure of their performance in the battle flow.
http://www.youtube.com/watch?v=xm11yAXeeggAlso, this is the first time I've heard of dancing being a good measure of unit maneuverability and fluidity.
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