Why'd they need to kill Telemachus anyway?

I mean, Antinous still defeated Telemachus (even tho he had Athena's help) one on one and there's like 108 of them.

Now man was out on his diplomatic mission, no one was guarding Penelope's door, so why didn't they just go for it instead of wasting their time shouting all of the plans in a hall?

(Not saying they should've, it's just that the suitors, and the whole 108 of them, don't seem very bright)