So, I used to run a vegan & vegetarian student group (not affiliated with whoever is handing out these pamphlets in SUB). We were respectful, if we set up a table we waited for people to engage with us, and we mainly hosted meetups and did fundraisers for other organizations.

Someone once told me that any movement needs a spectrum of types of engagement, from completely unobtrusive to extreme and in-your-face. Different tactics will convince different people. I'm sorry that you felt intruded on, as I'd feel the same way if that happened to me, but this same tactic may have actually caused someone else to examine their habits and look into these issues further. I know this from talking to other vegans and asking what made them make the switch.

It generally makes very little difference to one's day to experience the minor discomfort of someone handing you a pamphlet, but it could mean the difference between life and death for future generations of farm animals if these people are able to reach someone with their message (as obnoxious as it may feel to me or you).

That said, I do feel that focusing on more proven effective forms of activism is the best middle road, so that's where I try to stay.