Marco Falke points out that if the parent is RBF, this child inherits it. However, Matt Corallo points out that you can block RBF with a large-but-lowball tx. Peter Todd explains that the rule preventing bandwidth usage DoS attacks on the mempool by dropping it an attacker can repeatedly broadcast and replace a series of transactions to use up tx relay bandwidth for significantly lower cost than otherwise. This rule is against miner incentives (assuming mempool is full), and makes things more complex than they need to be.