Cold approaches are out because a) people will respond poorly to negative people and b) you won’t make them anyway
So right there, by having a shitty attitude, you’ve functionally cut yourself off from 99% of the ways of meeting new potential partners. Warm approaches are out because you have fewer friends who can connect you to their social networks.
Worse, pessimists deal with greater levels of stress and anxiety. It takes longer to bounce back from failures and mistakes, meaning that their performance takes an even bigger hit over time. That stress and anxiety also has a negative connotation with relationships- the higher your levels of stress and anxiety, the shorter and more contentious your relationships are.