The positive semidefiniteness of Laplacian matrices corresponding to graphs with negative edge weights is studied. Two alternative proofs to a result by Zelazo and Bürger (Theorem 3.2), which provides upper bounds on the magnitudes of the negative weights in terms of effective resistances within which to ensure definiteness of the Laplacians, are provided. Both proofs are direct and intuitive. The first employs purely geometrical arguments while the second relies on passivity arguments and the laws of physics for electrical circuits. The latter is then used to establish consensus in multi-agent systems with generalized high-order dynamics. A numerical example is given at the end of the paper to highlight the result.