If you don't understand how bitcoin works, then your opinion on the matter isn't very important.

If miners (or pools) refuse to include fee paying transactions and replace those transactions in the block with their own transactions it is not free.  It costs the miner (or pool) in at least 3 ways.

1. They still have to run the equipment to perform the mining. This has a cost associated with it, and they need enough revenue to keep it going.  The more revenue their competitors get, the more hashing power their competitors can afford which increases the profitability of their competitors and increases the mining difficulty.  Eventually the attacking miner (or pool) is operating at a loss.  When they lose enough money, they can't afford to continue to run and have to shut down.

2.  They lose out on the transaction fees from the transactions they refused to include.  This is lost revenue, and other miners or pools that choose to include those transactions will be able to afford more hash power, thereby making the attacking pool less relevant.

3. If their block gets orphaned, then all those "spam" transactions can be confirmed by some other miner or pool.  As such, they can pay a very hefty fee for playing such a game and taking such a risk.  Eventually this additional revenue for the "honest" miners and pools will allow them to afford more hash power, thereby making the attacking pool less relevant.

The only way miners could be successful in such an "attack" would be if there was a cartel of miners (or pools) that controlled significantly more than 50% of the hash power.  They could then all agree to exclude low-fee paying transactions and avoid mining each other's "spam".  If this occurs, then bitcoin is already a failure.  It won't matter if we have SegWit, Unlimited, Classix, XT, or something else.  Satoshi explained in the whitepaper, and it is clear to everyone that understands how bitcoin works that if an entity controls significantly more than 50% of the hashpower, they can take full control over which transactions get confirmed and which don't.  They can also roll back blocks several deep if they like.