serious question why is it generally frowned upon?
look if you're playing for lineups and your team knows this then they will not be hard defending site lol, lineups are an almost guaranteed round win unless the enemy team has no counterutility or doesn't push the guy with lineups. All you need to do as a team is defend the guy, and it's a lot harder for a team to retake a lineup setup because they have more space to clear. not to mention leaving a retaking teammate defenseless while he defuses.
if you are at a man advantage and are in a good lineup position it pretty much means you only use the money needed for the lineup utility, and you are less likely to lose shield/gun money because you're not actively fighting the enemy.
there's a reason DRX plays for lineups. They are almost a guaranteed win with little risk.