The best defensive players are always a bit pyscho. The better ones are looking to inflict pain. Seriously, look at any all-time greats at the defensive positions with maybe the exception of cornerback (Deion was sssooofffttt, although he is a borderline starting all-time CB).
safeties as well, consider such people as Deck (with an i) Butkus, probably the worlds greatest MLB ever seen, he said it pretty good "I wouldn't ever set out to hurt anyone deliberately unless it was, you know, important —like a league game or something."
You take steroids because you want to win and/or be a greater player so badly that you're willing to jeopardize your health, cheat, and break the law to improve yourself as an athlete, not because you don't care about winning. If anything, it's symptomatic of caring too much.
Some athletes get two year bans, but not all. NFL players are pros too. And losing a quarter-season for a first offense is plenty tough. Merriman could have made an honest mistake, for which ending his career would be an awful penalty.