That's why PoW provides a 51% mechanism.
It works both ways, any 51% attack can be 51% attacked.

I'd rather add some PoS checkpoints on top of bitcoin

51% mechanism is what allows to challenge the status quo, thus enabling competition for power.
Just sitting on your money in PoW does't give you control over the system, just engaging in the competition for control doesn't bring you money as mining is normally a break-even game. Thus money and control become orthogonal, which results in a dynamic system without asymptotes. In PoS you get both in a nice single package, which saturates fairly quickly.

Hybrid systems are more tricky beasts, thus they need to be studied closely. I'm concerned that saturation in PoS aspect of the hybrid will at some point begin to negatively influence the competition on PoW side.

For those unaware, there have been some serious
hybrid PoW/PoS proposals for Bitcoin, which you can find here:
https://en.bitcoin.it/wiki/Proof_of_Stake

You just don't get it do you?  Bitcoin is becoming more centralized as time goes on.  Mining is becoming increasingly corporatized.  The users of Bitcoin are separated from the security of the chain.  This is against everything Satoshi wanted in a currency.  The goal of Bitcoin was to place the monetary power back in the hands of the people.  Bitcoin has evolved into the monster it was meant to replace.

You can criticize NXT's initial distribution and claim it is "centralized" because initially the currency was held by 73 individuals, but at the end of the day PoW vs PoS argument comes down to trust.

Do you trust external agents not to overpower BTC's hashpower?  Only a fool would believe that a government doesn't have the resources to control Bitcoin.  The bitcoin hashpower held by individual people (not corporations or pools), who are legitimately concerned with securing the chain and not merely profits, will never be enough to prevent an attack on BTC.  The BTC chain might not be destroyed by these "attackers" but altered or restricted.  What if a government decided to freeze certain accounts?  They could easily coerce the corporate and pool miners to enact these changes.  The individual miners and currency users would be helpless to stop it.

Do you trust that the original NXT stakeholders are actually individuals committed to decentralization and continuing the legacy of bitcoin?  Seeing that the NXT IPO drew very little attention, I figure that the original stakeholders are actual individuals and not corporations, bankers, private equity or governments.  That means the chain was originally secured by individuals who were drawn to the movement by the original ideals of Bitcoin.  Since the start of NXT, the holders have obviously changed.  A good portion of the original stakeholders have sold out.  Who did they sell to?  Do you think they sold to the corporations, bankers, PE and governments?  I'm sure some did, but does this allow for these entities to attack the chain?  If together and working in concert these groups acquired over 500 million NXT, then yes.  If not though, the chain is secured by decentralized individuals.  The more individuals that join NXT the stronger and more resistant to attack it becomes.  Soon it becomes extremely difficult to purchase enough stake to attack without driving up the price to a ridiculous amount and it becomes equally difficult to coerce enough individuals.  When NXT forms its economic cluster, the stake requirements to attack will rise to 90%.  This makes acquiring the required stake to launch an attack practically impossible especially if you consider that some stakeholders will just never sell.

So, do you trust external agents to not to overpower BTC's hashpower or do you trust that NXT's stakeholders are actually legitimate individuals?

This thread clearly shows how bored people are these days, trying to generate value by talking 

Bitcoin will either never change to PoS or such a change won't occur till 2024 and beyond.

I suggest you gamble all you want with PoS. Seem like you are a Nxt proponent.... that currency is dying right now if you haven't noticed. Dropped from spot 5 to 8 in market cap and soon to be overtaken by Bitcoin assets like Counterparty! Ethereum, Counterparty and possibly Storj will likely overtake Nxt in 2016, expect it will drop further in market cap.

Fiat really is an archaic form of PoS.  Centralization also has advantages over decentralization. Decentralization is very costly and inefficient.

Ohh goodness, they really should bring back the rule of sand boxing newbie accounts . You are ignored my friend.

Who's plans were misplaced and where were they supposed to be?

This is mostly true and why I am a big fan of PoS coins. I think every Central Bank should have one.

Money can change ownership much quicker than mining rigs. It's much easier to find a mining farm if you want to control Bitcoin (hint - it consumes a lot of electricity).

Define "weaker" in your suggested context and provide historical evidence to support this claim.

Just like digging out gold, it seems the labor wasted are unnecessary, but it does solve the origin of value problem: The man who create money must pay fair price to get it, otherwise everyone will be just creating money and no one will be working

To control the majority of hash power, you must put real resources and might still fail due to slow in movement, it is much more difficult than controlling a few stake holders. Imagine that once bitcoin is becoming POS, then top 10 stake holders will immediately enter the watch list of CIA

This is for PoS coin stake holders

It is not wasteful, it is a must. You can't create money out of thin air like fiat money, that kind of scam must stop, this is the point of bitcoin

PoW hash rate domination are all temporary and can be changed quickly, we have seen many times old hash rate king been knocked down by new mining pools/farms