Well-meaning people are reluctant to support active debris removal, because debris removal vehicles can be considered weapons. He who can net, hook or otherwise capture a satellite can do so both for peaceful and for hostile purposes.
Well-meaning people also acknowledge that states might have good reasons to resist that satellites under their supervision and control be interfered with by other states. If satellites under the supervision and control of one state is captured by another this might mean that technology will be stolen and for security relevant satellites, such as spy satellites, this might be critical.
Space lawyers explain that the space treaties mean that the consent of a state which has supervision and control of a satellite is required for another state to remove it.
The concern about debris removal vehicles being also weapons is very real. Yet, it can be argued, as does my friend David Koplow, that all satellites are weapons because as long as you can steer them you can steer them in such a fashion that they will collide with and destroy enemy satellites. However, I do not think it is quite as easy to use satellites as weapons as one may assume, because of the imperfections of conjunction analysis and because the unwilling target may take evasive action, and that is particularly true in relation to removal vehicles that not only has to find the target but also has to capture it. It can thus be argued that removal vehicles are less dangerous weapons than normal satellites that may be used for kinetic impact à la a missile.
The technology theft argument is also less persuasive than one would think at first sight. An unsteerable satellite will often be in that condition because it has run out of fuel. That means that it is old, and probably not very interesting technologically. But even for unsteerable satellites that may have malfunctioned for other reasons, and hence might be younger and with more interesting technology, it is limited what can be learned through the cameras on the removal vehicle, and capturing and bringing it back to Earth would be illogical in a debris removal sense since the rational thing to do would be to put the dysfunctional satellite into a graveyard orbit.
As for space law, it can be argued that the space treaties did not aim at the debris situation but at things like liability and unhampered use. Analogies to the law of salvage and to general principles on avoidance of harm may lead to the conclusion that the consent of the state of supervision and control is not necessary to remove debris, some of which might not be identifiable in advance of removal if a fragment only.
If you have residual concerns despite the above arguments there is an elegant solution, a solution that in any event might be the best one to tackle what is in the final analysis a community task (and we can then discuss the financing). The creation of an international organisation dedicated to debris removal would mean that consent to removal would have been given a priori, the concern about spying would be allayed by creating a corps of international removal engineers adhering to a behavioural code similar to that of IAEA inspectors – and giving the state whose satellite was being removed a right to accompany and ‘inspect’ the removal process would further buttress this.
Finally, the concern that removal vehicles could be understood as space weapons and that their introduction would open the floodgates on space weaponisation could be eliminated by banning all removal vehicles except those operated by the international debris removal organisation.
For such a solution to come about the international community would have to come together in a big way, and although one should not be defeatist, this may appear unlikely at the present time, even if all agree that debris is an almost existential question for the space community. So perhaps you just have to make do with my arguments why active debris removal is legal and unconcerning even without a new treaty and a new international organisation!