Staking coins = gaining interest. Because this is a default no-cost options, everyone is doing it thus the "value" present on the network will be split across existing stake and new issued coins for the stakes (if the coin is not fully mined). Thus, you are not actually gaining "value" but you spread it across increasingly more coins, something called inflation of monetary mass.

Not staking coins means your value is diminished because the individual tokens are worth less. Or compared to stakers, you don't gain as much. Being a zero sum game without value influx/outflux, not staking coins puts you in a constant loss of value.

Why would you hold a coin that holds it's value like Bitcoin or one that loses value like Peercoin? Oh, you only want to use it when really needed? Why would anyone provide counterparty for your need if they can lose if your demand is lower than expected.

The main argument against PoS is the old "the rich get richer". Not a problem with that, except they do NOTHING but freeze coins, there is no risk involved inside the system. They don't buy hardware, they don't pay utilities, they don't hire people. They just do nothing and get rewarded. You think Bitcoin hodlers are gaining rude profits by doing nothing? PoS makes it even worse. But again, without actual new value added into the system, the existing value is spread around to the existing coins (think stable market cap) and each coin is losing value. There is a difference between theory and application, just like Communism, some things look great on paper but fail the test of reality.

As for providing extra services... what are the benefits of using NXT/MSC/XC?