So the Borer is in a bit of a tough spot at the moment. They're considered antags, but the vast majority are friendly towards the crew and are more often than not a good thing to have. I believe that borers should be a neutral, somewhat hostile entity that needs to be treated less like a pet and more like an actual potential threat to the station. Sure, there'll still be benefits to having one in your head, but the borer should be more interested in its own affairs than the host. To fix that, I believe the borer needs new objectives and/or mechanic changes.
The first objective idea being Create and defend a nest till the end of the shift. This objective essentially requires a borer to find a location for a 'nest' structure, get a host there to build the nest, then have the host sit within the nest for a certain amount of time before becoming assimilated by it, causing the host to (At their choice) either be killed or turned into a borer (defaulting to kill if they don't respond soon enough), and the original borer to be ejected from the body. The nest acts as a permanent borer spawn, creating new borers about every two minutes. Once created, all other borers are informed on its location and given the objective to protect it. Unless the nest is destroyed, no other nests can be built. People infected with borers will be 'struck by sudden guilt' when attempting to harm the nest and won't be able to damage it. Essentially, the more people infected, the harder it'll be for the crew to destroy the nest. Of course, the crew can accept the one sacrificed crew member for an infinite supply of chem injector implants, but they should also consider the fact that the borers may hijack the crew if their nest is threatened.
The second objective idea is Infect enough people to establish the hivemind/Infect as many individuals as possible. This objective requires the borers to infect a certain number of people (About 10, depending on server pop) in order to establish the 'Hivemind'. Borer telepathy will not be altered. Unlocking the hivemind will give the borers new powers that scale based on how many people are infected. Thinks like faster chem creation, longer stun and control duration, or a HuD to identify other infected individuals. The downside is that the increased neurological activity from the borer slowly damages the hosts brain. Now, the borer could use their chems to heal this damage, or they can wait till the host becomes brain dead, which allows them to assume permanent control. The other downsides being that, once the hivemind is established, the borer will always show up on Health HuDs, are are more vulnerable to sugar.
The final idea I have, (Which should require minimal coding) is to randomly give borers simple miscellaneous objectives. No assassinations or grand thefts, but things like 'Consume a certain food' (May or may not be toxic to the host), 'Hug/knock over/punch a certain number of people', or 'Make your host wear certain clothes upon escaping the station'. They're borers. We know next to nothing about them, where they're from, nor why they may want to do all this weird stuff. These are minor things that'd give borer players more to do than just reproduce, and it'd make things interesting for the crew as people wonder why the captain is running around in the clown outfit while hugging everyone. If a lore reason is needed, it can be that the borers are 'collecting experiences and memories of a certain kind to benefit the hivemind'. This isn't gonna make all crew hate borers, but it'll be enough to actually make them disruptive to station affairs.