In this case I think it's OK. (I have no financial interest in Cardit, personally think the fee is too high for the value I place on getting more miles, and do not expect to use it.) He didn't bring up the topic. His company was criticized for offering no value, indeed for ripping off the innocent public. His reply, whether or not one agrees with its content, was reasonable and calm.

There are many instances of this throughout FT, including airlines/hotels defending their policies from criticism (some fair, some not) and a thread that comes to mind involving a motor built into the front landing gear of an aircraft to move it on the ground. I'm not a moderator, but I see no grounds for disallowing his post.

If posts like this were not allowed, anyone could criticize anything for any reason or no reason (after all, criticism isn't forbidden, only promotion) and it would be impossible for anyone else to respond with any content.