What's wrong with using protium catalytically in a fusion reactor?

P-D fusion results in 3He, then D-3He results in a P+D+D turning into P+4He. Isn’t that net energy positive at a relatively low temperature without too many neutrons? Some D+D side products will happen but if my reading of rates is right then there’s a temperature range where D-3He will happen a lot more and the D-D reaction will release neutrons which want to take energy out of the core and having 3He in there to act as a neutron poison will make it produce more energy and keep the heat inside. The obvious potential pitfalls are if P-D allows too much energy to escape as a gamma ray or neutrino or if D-D happens at a fast rate at a lower temperature than D-3He.