Thank you Dr.Albert. By reading a bit further, it seems part of the reason why removing the recombinant sequences is not advisable is because it’s difficult to distinguish whether the novel sequence is due to the recombination process or selective forces exerted on it, which might affect the inference later.
But another paper also mentioned that evolutionary inference can be misled if recombination is not taken into consideration, because recombinant sequences cannot be explained by the same phylogenetic tree as the original sequences. (Kosakovsky Pond, 2006)
Two claims seem to be conflicting with each other.
Didelot, X., & Maiden, M. C. (2010). Impact of recombination on bacterial evolution. Trends in microbiology, 18(7), 315-322.
Kosakovsky Pond, S. L., Posada, D., Gravenor, M. B., Woelk, C. H., & Frost, S. D. (2006). GARD: a genetic algorithm for recombination detection. Bioinformatics, 22(24), 3096-3098.