I guess that depends on whether or not you consider bot-promoting to being doing good work. Personally, I don't, but I'm sure others think it is a reward for being not quite good enough to actually earn the promotion.
From the threads where this suggestion seems to have come from, I think the original idea was as much, if not more, about allowing teams in micro nations to be able to choose to start in lower leagues rather than being forced to start in D.II or even D.I and be at a considerable handicap. In those cases, it has often been the case that a new user would join, realize they have no hope of competing because they lack everything a team needs at the league level they are placed in, so leave. Now they at least get a partial season of competing against mostly bots before they might end up being bot-promoted up themselves.
As Marin said, you can expect that most of the new users who choose to start in a higher league in the larger countries will be relegating down on their own merits. So a new user joining with a D.II team really isn't going to impact D.III promotion, but it will remove the cascading impact which a bot would have had on D.IV and D.V.