The sidechain networks, from my understanding, is for thousands or millions of transactions a day, using their own coin.
Because of this, Bitcoin/bitcoin can stay the way it is and not have to hard fork to handle an increase in block sizes (20mb debate).
The idea is to keep it tied to bitcoin and will use Bitcoin network to do 1 or 2 major settlement transactions a day.

The altcoins that currently exist are not directly tied to bitcoin, but can be bought and converted into bitcoin.

But yes, I do think when it comes to the sidechain networks, they are instamined, controlled, and not decentralized.
But I may be incorrect on that.

Ultimately, the sidechain networks are a work around from increasing the Bitcoin block size.

Yes, in theory.
It is possible there could be competing sidechains in the future and venders could use multiple ones like Visa, Mastercard, etc.
The vendors could choose which ever sidechain network they preferred. One could be tied to Coinbase, another could be Bitpay, or etc.
Or it could be that one beats them all out and there is only one official BTC sidechain network for vendors, in the future, when the time comes.

The debate is whether Bitcoin should be "the" coin for all global transactions, or should be "the" final settlement coin, that all other systems feed back into.

I don't get side chains.  Can somebody post a example of how one might work?  Would the coin used be bitcoin or something different?

the dev behind it are the four dev that work on bitcoin, one should trust them more than a random dev on the altcoin section

also bears in mind that sidechain are empty, you just fill them by moving your bitcoin, they are alternatives blockchain that are waiting to be used, for their unique features

here a good explanation http://gendal.me/2014/10/26/a-simple-explanation-of-bitcoin-sidechains/

basically a interaction between multiple blockchain, like multiverse, if you allow me an analogy


a summary

The sidechains ideas is this:

Send your Bitcoins to a specially formed Bitcoin address. The address is specially designed so that the coins will now be out of your control… and out of the control of anybody else either. They’re completely immobilized and can only be unlocked if somebody can prove they’re no longer being used elsewhere (I’ll explain what I mean by this in a minute).   In other words, you’ve used the core bitcoin transaction rules I described above to lay down a specific condition that the future owner – whoever it ends up being – needs to fulfil in order to take control

Once this immobilisation transaction is sufficiently confirmed, you send a message to the other blockchain – the one you were wanting to use. This message contains a proof that the coins were sent to that special address on the Bitcoin network, that they are therefore now immobilized and, crucially, that you were the one who did it

If the second blockchain has agreed to be a Bitcoin sidechain, it now does something really special… it creates the exact same number of tokens on its own network and gives you control of them.

So it’s as if your Bitcoins have been transferred to this second chain. And remember: they’re immobilized on the Bitcoin network… so we haven’t created or destroyed any…. Just “moved” them.

You can now transact with those coins on that second chain, under whatever rules that chain chooses to implement.

Perhaps blocks are created faster on that sidechain. Perhaps transaction scripts are “turing complete”. Perhaps you have to pay fees to incent those securing that sidechain. Who knows. The rules can be whatever those running that sidechain want them to be. The only rule that matters is that the sidechain agrees to follow the convention that if you can prove you put some Bitcoins out of reach on the Bitcoin network, the same number will pop into existence on the sidechain.

And now for the second clever part. The logic above is symmetric. So, at any point, whoever is holding these coins on the sidechain can send them back to the Bitcoin network by creating a special transaction on the sidechain that immobilises the bitcoins on the sidechain. They’ll disappear from the sidechain and become available again on the Bitcoin network, under the control of whoever last owned them on the sidechain.

The thing people are missing is that most users will stick to transacting in BTC, period. It's a very nice idea, i am actual porting and running a testnet by tonight but don't you see, instead of making BTC easier to use and explain, it just got a thousand times harder. This in no way improves the 1 MB situation or the mass adoption goal.

I think that this release was hurriedly pushed forward to try and counter the advocates of the 20/8 MB increase, even some of the stuff i am looking at now make no real sense. I'll keep trying to grasp it, maybe i'll change my mind, but i'm so far unimpressed (with regard to fixing tx issue).

If anyone wants to read an example of sidechains, here is a link from reddit I just read.
It seems like a good example for anyone who is completely lost.
http://www.reddit.com/r/Bitcoin/comments/396m1y/a_simple_way_to_think_about_how_sidechains_work/

Pretty much this. Altcoins are just a hindrance, people are creating them as pump and dump in order to earn quick money almost in 100% cases.
Most of them are copy paste or existing code without any changes beside name of the coin. Instead on focusing our attention on altcoins why don't we focus and upgrade bitcoin?
It would beneficial for us a lot more than creating new altcoin everyday. I think going pro sidechains are also not the way to evolve... Only pure bitcoin is the way. Stop deviations.

 - Gold relies on physics for backing.

 - Fiat relies on a judicial system for backing.  (legal tender laws and enforcement.)

 - Bitcoin relies on math for backing.

 - Sidechains rely on Bitcoin for backing.

Sharp-eyed viewers will note that sidechains which are properly implemented actually do not need POW or POS (proof-of-work, proof-of-stake) to have an autonomous backing store because they rely on something else, though force of habit will probably make most of them make some use of certain of these mechanisms.  What sidechains need desperately, however, is for that their backing is rock solid.  I hypothesize/hope that it provides sufficient incentive to keep Bitcoin healthy, but this relies on sidechains themselves to be widely geo-politially distributed which is entirely possible and even likely.  And if not likely, at least the best hope.

Here is a very real danger to Bitcoin which nobody talks about:  Sidechains could relatively easily 'swap out' their backing store to something else.  If they did so en-mass Bitcoin could suffer or even die.  Should that happen, however, it would probably be in a situation where that was a good thing, and the value base may well be snapped from the extinct blockchain.

i think the value should be 1:1 with bitcoin, and if one of the sidechain value, is increased the ratio should still remain the same, so bitcoin should increase too in value(it is as if they had bought bitcoin when they buy each saidechain counterpart), this should avoid any issue about your concern