This needs elaborating. Why would the coinbase txs be treated any different from other tx?
If by invalidating a tangle fragment a miner can increase his profit
Do you mean that invalidating tangle fragments increases the chance of
a coinbase tx getting confirmations? Why would that be the case?
And wouldn't that apply to any tx that someone wants to see confirmed badly?
then he will do that. It's easy to invalidate a branch if you split your tokens and include small transactions into all branches, you can use any to doublespend.
This argument is not convincing, since you can just replace "miner" by "attacker",
and face the same problem?!