I would like to say this is not something I would do myself, nor is something I would personally condone.

With the above being said, someone has sMerits because they ultimately previously made a post someone thought is deserving of merit. As such, I consider sMerit (assuming they are not spending sMerit they have resulting from what they received from being a merit source) to be their property, and I am not a fan of telling others what they can and cannot do with their own property.

The underlying reason why others believe sending merit to your alts is because of the conflict of interest. However, as previously mentioned, the ultimate reason why someone has sMerit to spend in the first place is because someone thought they made (a) good post(s) in the past; the reason someone will send merit to themselves is to rank up, however if someone earned merit in the 1st place, there isn't any real reason why someone couldn't make good posts with their alt to earn merit from someone else.

Back to the topic of conflict of interest, a bigger concern is when people send merit to someone who they have a business (or other) relationship with. If there is a relationship between two people, there may be financial (or other) reasons why someone is giving merit to that person. It could easily be argued that the merit sender thought the post in question was deserving of merit. Unlike with cases of sending merit to yourself, it would not be trivial for the receiving account to earn the merit if there is already merit to spend in the 1st place.