I say play hard. The way to be "kind" is to guard your words after the game.
e.g.
Opponent: "I got slaughtered, eh?"
You: "Sure did".
Instead, something like...
Opponent: "I got slaughtered, eh?"
You: "Hey, I just got demolished by a stronger opponent too. Just part of learning."
Im not à very good chessplayer, but i play every game as good as i can. A few months ago i was so happy that
i had won against a 1540 rated player, that i losed the next game against à 1098 rated player. Since that im
sharper. Conclusion:be always sharp. Against à good player you can win much points and against à weaker player you can lose much points, i think we all hate it more when we lose against à weaker player, so thats the reason i dont play less good against weaker players.