The new "feature" called RBF being added to some versions of Bitcoin doesn't just let you increase the fee.
It also lets you:
- change the recipient
- change the amount
... after sending the transaction.
So instead of calling it RBF, it might be more accurate to call it CRCA (Change-the-Recipient-and-Change-the-Amount).
Sounds crazy, huh?
I guess they couldn't name it Change-the-Recipient-and-Change-the-Amount, because then everyone would immediately see how dangerous RBF is, and users would refuse to install a any code which included it.
But fortunately you now have a choice.
You don't have to install code which includes RBF.
The only code which includes RBF is the code being released by by the Core dev team - Bitcoin Core version 0.12.0.
Meanwhile, RBF is not expected to be included in code released by the other dev teams, who are more serious about avoiding such controversial or confusing "features" which don't enjoy broad consensus from the community.
These other dev teams include:
- Bitcoin Classic
- Bitcoin Unlimited
- Bitcoin XT
So remember, you do have a choice.
If you don't want code which includes Replace-by-Fee (or Change-the-Recipient-and-Change-the-Amount), then you don't have to install Bitcoin Core 0.12.0.
When you do decide to upgrade, you can simply install a release from one of the other dev teams - and then continue use Bitcoin as it was originally intended, with no confusing or dangerous options in the interface allowing people to change the recipient or change the amount after sending a transaction.