From the whitepaper:
assets, which carry their own semantics.
As a Bitcoin holder I fail to see why I wouldn't prefer such a sidechain to one that is relying on transaction fees for mining, other than possibly ideological reasons, which I doubt will have much practical effect. Fees plus token should be more secure than fees alone, assuming any value for the token.
The additional token may divert mining resources away from MC, causing MC to be less secure. Of course the additional token could bring additional mining resources into the network.