What are the economics for the nodes that are confirming the block (including which tx are valid and which not)? Couldnt I set up thousands (or millions, whatever is necccessary) of nodes that then are the majority that can confirm the false block suggested by the malicious miner?
That's called "creating a fork".
You would have created your own separate network that would allow those false blocks. If you could convince others to use your special software that allowed those blocks, then you will have created your own separate coin that is not bitcoin. Essentially this is what all the "altcoins" are. They all create blocks that are not valid blocks in bitcoin. They convince others to use their "bad block" accepting software, and now they can send coins to each other on their network.
Bitcoin is not a democracy system. The majority doesn't decide for everyone else. It isn't even a super-majority system. It is a
consensus system. This means that if you want to make a change to the basics of the protocol, you need
everyone to agree. Otherwise the network splits into two factions. The consensus that accepts the change and the consensus that rejects the change.
Remember I said "
Every peer on the entire network". It doesn't matter how many nodes you set up on your non-bitcoin network that accept the change, as soon as one of those nodes try to send the block to a connected peer on my bitcoin network, that peer will attempt to validate the block. It will see that the block is not valid and it will not add it to its own blockchain, and will not relay the block to me or anyone else on my bitcoin network. Meanwhile, the miners on the bitcoin network will continue creating valid blocks.
If your network has more total hashing power than all the combined hashing power in the bitcoin network, then you will eventually stop accepting any blocks that are created by bitcoin miners (since each block refers to its previous block, and your network will have a different, newer, block). Their will be tow permanently forked blockchains, the bitcoin blockchain that I and my peers have, and the non-bitcoin blockchain that you and your peers have. Those blockchains will be identical up to the point of the fork, and any unspent outputs from before the fork can be separately spent in both my system and yours. Unspent outputs that are created after the fork will be only spendable in the fork where they are created.
If your network has less total hashing power than all the combined hashing power in the bitcoin network, then you won't create blocks fast enough to stay ahead of the bitcoin blockchain. Every time the bitcoin blockchain exceeds your blockchain in total difficulty, your network will orphan all the blocks that it created and replace them with the valid blocks from the bitcoin blockchain. There will be no incentive for anyone else to mine or participate on your network because confirmations on your network will keep being thrown out, and mined coins will continuously cease to exist. To avoid this problem, altcoins disconnect from the bitcoin network. They fork the blockchain at the very first block, create a network that not only mines its own blocks that aren't valid on the bitcoin network, but also reject any block that would be considered valid on the bitcoin network, and communicate on a separate connection port so they don't accidentally communicate with bitcoin peers.
If a majority is not enough and all have to agree,
It is not. You need everyone to agree. 100%.
If there are two people in the entire world who decide they don't like the block accepting rules in your system, then they will connect to each other, and continue to reject your blocks and create and accept their own.
then couldn't I damage the network by being a node that refuses to confirm blocks that are valid?
No. The network would simply ignore you and your invalid blocks.
I also read this
https://en.bitcoin.it/wiki/Double-spending "If the attacker controls more than half of the network hashrate, the previous attack has a probability of 100% to succeed."
Why? If the attacker has exactly 50% of the hashing power his chance of finding the next block sould be 50% not 100%?
Correct.
In order to reach consensus, each miner builds blocks that have a reference to a previous block. As the blockchain gets longer, this implies that more and more miners have accepted a particular previous block in their blockchain, and creates a financial incentive to choose to build on the blockchain that contains this particular block instead of some other blockchain that is missing this block.
However, as your hashing power gets higher, you have an increasing chance of finding the next block, which implies that you find an increasing percentage of all the blocks that are found. When you reach 50% of the hashing power, you are finding approximately half of all the blocks. If you can exceed 50%, you are now able to find blocks faster than everybody else combined. Once you've done that, you can choose to create and use software that refuses to accept any blocks from any other miners. You can choose to only build new blocks that have a reference to the last block that
you found. Since you solve more blocks per day than everybody else, your blockchain will always be longer than any blockchain that includes blocks created by other people. This means that you will continually orphan any blocks solved by any other miner as the network accepts your longer chain as the consensus chain. Since you get to choose the blocks that remain in the chain and the blocks that are orphaned, you can orphan blocks that include particular transactions and confirm in your blocks a different set of transactions that spend the same inputs elsewhere. Of course this will only work if you create
valid blocks that the rest of the network accepts.
An attack like this allows you to choose which valid transactions are confirmed and which valid blocks are accepted into the blockchain, but it doesn't allow you to change the protocol.
Regarding using google to answer the questions above: Show me where a google search that directs me to an answer of those questions above and I dont ask anymore. Keep in mind that for someone that is not as tech savvy as some here and who also doesnt yet completely understand bitcoin in detail it is often not possible to answer the questions above by guessing the answer from implications following from some writing that is not explicately focused on those questions.
If you haven't read the bitcoin whitepaper yet, you really should. It explains a lot about how bitcoin works and helps you understand things well enough to ask questions that actually make sense.
