WolfishMusings,
The question is, should a mamzer(ess) marry and have children. It is commonly expressed how terrible it is to bring mamzerim into the world.
I think the terribleness of bringing about mamzerim you are referring to is primarily directed towards the initial circumstance. After the fact, if “containing the damage” was Hashem’s top priority, why would He permit mamzerim to marry at all?
In other words, what Hashem hates is the behavior that causes a mamzer in the first place, as opposed to the mamzer himself.
1. If a mamzer wants to prevent an increase in the number of mamzerim in the world, can he willingly not marry and have children?
For mamzerim to find permitted and suitable potential spouses would be miraculous; why should they deny themselves happiness due to sins that were not their fault?
2. Should we discourage known mamzerim who do want to marry from doing so, again with the goal of not increasing the number of mamzerim in the world?
I think the focus would be better placed on preventing the sins from which mamzerim originate.
3. If he wants to decrease the number of mamzerim in the world, can he consider suicide?
Umm, what? Where in the Torah is it ever suggested that murdering a mamzer is permitted?
If the answers to any of the above questions is no, how do we reconcile this with the idea that HKBH clearly does not want mamzerim?
I think your focus on this issue is a bit off. What HKBH does not want to happen is the circumstances that produce a mamzer ab origine, e.g., adultery, not the mamzer per se.