Many people, me too, think he is wrong.  I will stick to Bitcoin, and if people will exchange the bitcoins they bought from me to some altcoin, I don't have any problems with that.  In the past I got many requests to sell litecoin, primecoin, scamcoin and whatevercoin.  My answer has always been the same: I buy and sell bitcoin, and if you want something else, it is very easy to exchange the bitcoins to something else elsewhere.  As you see from the short list of businesses wanting to switch to an altcoin based on different consensus rules, the great majority will stick to Bitcoin.

I think many miners will switch back to Bitcoin as well, since their newly minted coins will only be accepted by a very few merchants.  If an exchange try to sell the altcoin as Bitcoin, they will certainly get sued by people who discover the coin they bought won't be accepted by merchants accepting Bitcoin.  This can lead to severe losses.  I regularly buy lumps of 100 BTC which people send to my autobuy system with no prior notice.  If someone send some altcoin to the same address because the address format is the same, they may have lost a lot of money.  100 classiccoins, unlimitedcoins, bitpaycoins, XTcoins or whatevertheyarecalledthisweekcoins will probably not be worth anyting, but you get my point.  People are going to lose a lot of money on the confusion.  As a bonus to miners coming back to Bitcoin, the difficulty will get significantly lower.

My Websters Unabridged Dictionary of the English Language defines consensus as a "general agreement or concord".  In Bitcoin this agreement is defined in the software.

You misinterpret the general agreement among all bitcoin nodes as a wish from a specific "minority".   Which is actually the opposite of what he actually wrote:  "majority MUST NOT be able to override minority"  I.e. consensus is not what a minority wants, neither what a majority wants.  Consensus is based on the agreement which was there from the beginning.  Neither Bitstream or any short list of merchants, can overrule the general agreement which define Bitcoin and the bitcoin blockchain.  Neither can a majority.

Correct within normal rounding rules.  (If one or two won't change, it probably doesn't matter much.  As long as there is a significant chance of an SPV client contacting those nodes, especially if they have any mining power behind them, the security of SPV wallets will be severely compromised.  But people shouldn't trust SPV clients anyway.)

You don't get it.  Since this would change the general agreement, it would require cooperation from all bitcoin nodes.  Not just a majority.

Are you telling me you don't support this!?  Why do you hate children?  Do you kill babies for a hobby?

Actually the explanation there is just a longer version of mine.  Read it again, and see if you can understand it.

ROFL!  Read it again.  "To implement a hardfork, without a blockchain-fork, all users must switch to the new protocol consensually."

How many bitcoin blockchains do you think is adequate?  At least we will get rid of SPV clients by hard forking into many chains, but unfortunately you would then have to rely on either wallets talking to some central trusted node, or that everyone run full nodes locked to one specific blockchain.  (You don't want to risk another chain to take over if they gain more mining power.)

Old nodes will work just fine after a softfork, but merchants should upgrade.  SPV clients are mostly safe after a softfork as well, but both old nodes and SPV clients may see unconfirmed transactions which aren't valid.  (In a hard fork the invalid transactions would confirm in some chains, and the SPV client will see it differently depending on which node it connects to.)