If you go and try and hit someone then you deserve a red irrespective on whether you actually connect. Slattery actions are typical of the modern game. Slight touch then hit ground, otherwise the referees will ignore it. The problem is that referees wont give fouls if a player stays on his feet even if it impacts the players control of the ball.
St Mirren cant complain as all their usual tactics of bodychecks, leaving foot in, jersey pulls, multi ball placements, etc are as much as cheating as Slattery's actions. Every team will try or do anything to gain an advantage.
In an ideal world we take the moral high ground but why put ourselves at a disadvantage?