This is how bitcoin works. The network will adopt whatever the majority agree on in terms what transactions happened. As a result, you can't man-in-the-middle bitcoin and it remains secure even without centralized key signers, because you can increase your confidence by confirming a transaction with as many nodes as you want. This is how you validate a local block chain - you connect to enough other bitcoin clients in the swarm such that at some confidence threshold you agree your chain is the correct one. The usual number is 8 independent connections in the bitcoin network (both for blockchain verification and confirmation of transaction acceptance) because the probability of getting 8 bad actors agreeing to the same fraudulent transaction is mathematically demonstrated to be sufficiently low.

Note: that is (besides the 51% attack vector) the primary reason the bigger parts of the crypto scene won't call bitcoin truly secure. Because there is still a risk of insecurity, it is just abysmally small, and disrupting one node doesn't mean the degradation of the web of trust because as long as the majority still agrees on the correct state of affairs (and as a false block chain diverges it becomes more expensive to maintain that public facing fork to disrupt other clients).