You definitely have to put a lot of trust in people, I'm sure you are aware of those with not so like-minded intentions that wish to prey on the vulnerable people through Suicide pacts and the like, but besides that it is a good idea since humans are social at heart, even in a moment of CTB. Oh also, another con would be your friend or pact-partner backing out most likely from Survival Instinct (SI) or some other reason leaving you hanging, No pun intended