It's the theological equivalent of "eat your vegetables". The link to Penn's commentary explains it reasonably well: no one wants to tackle another person, but you'd do it to stop someone from getting hit by a truck. Likewise, if you're sincere in thinking educating others of the theological risks can save their life - like you're not just going through the church-on-sunday motions, personal feelings take a back seat. To them it's too important to let petty things get in the way.

Naturally, this can backfire pretty hard. But that's the cost of taking the faith seriously.