Here are two theories of how people make decisions.
One theory -- weighted decision making -- says that there are many factors that go into a decision. Each factor is given a weighting proportional to its importance, so it's not one vote per factor but rather the more important factors count for more. Then all the factors are added up, and the decision with the most support is made.
In this model, genes could have an influence in a decision for one side or another, and a 10% weighting, and thus would have some influence, and would sometimes tip the scales in close decisions. They could have a 50% influence in another type of decisions, and 90% in another. An environment could have different percent influence for each, and so on. Dozens of factors could be included. In general, there is no serious difficulty in proposing there's one more factor with a small weighting
In this model, the theory that genes have an influence, varying from 0% to 99%, and averaging around 50%, is plausible. It doesn't contradict anything about the model.
The second theory -- explanatory decision making -- says that decisions are made by conjecturing a set of possible decisions, and then criticizing each possibility. If only one possibility remains, that decision is made. If more than one remains, that is a significant problem (omitting details for brevity, just understand that this is considered a rare case). How options are ruled out does not depend on weighting the importance of anything. It is an all or nothing proposition -- either the option survives a criticism or it doesn't. (The only way it's not all-or-nothing is that we might propose a variant of an option which changes a few things in order to survive the criticism.)
In this model, we never add anything up to get a result. Nothing ever outweighs something else. Rather we always find a single explanation of why we think our decision is the best one.
In this model, the way to influence the decision making process is to offer conjectures, explanations and criticism. That takes thought, or pre-existing relevant knowledge. And influences are never 10% or 50%. Rather they are good ideas that are accepted (or accepted with minor changes) or they are bad ideas that are rejected in full.
In this model, the theory that genes have an influence on decisions, averaging around 50%, is incoherent. It's incompatible with this model. The only time genes could have an influence is when they encode ideas which could be considered in the decision making process, and then accepted or rejected on their merits (the result would be exactly the same if the idea came from a friend or a gene -- it depends entirely on what the idea is).