I am opposed on what I view as ethical/precedent-setting grounds as well as the cost. I hate the idea of butting in on the fates of billions of people so Fleetness can get a better budget faster.
Let's remember there are good reasons not to have two new members a year. Bringing in a new Member requires an enormous amount of logistical, diplomatic, and political work. It requires a review of laws and trade regulations. It requires psychological preparation for new citizens, and a media blitz campaign to make everyone aware of what it means to be a Federation citizen. It's a big, big deal and doing one a year is pushing it.
And you want to double all this work? Worse, you want it done sloppier, faster, with less care, and with less experienced people on the job because you can't have your best people in two places at once.
Narratively this is a huge imposition and will result in additional fuck-ups and problems, guaranteed. So balance all those benefits to Starfleet against that.
