Yeah, no shit it's strong logic. Besides a blood test, how else do you determine if someone is using steroids?
I'm not well versed in all the different methods, but there are several (hair and urine for example). I've only ever been required to give a urine sample when competing. But another option that is hard to beat would be random testing.
Of course, once you get to know someone and see how they spend their day and the things they do in their personal lives that also provides a lot of insight. For instance, if you were roommates with any of the people you're accusing. Not that they would ever want to live with you, or you with them.
Point is, you shouldn't be throwing around baseless accusations when there isn't anything to back them up. That's why they're called opinions, because they're based solely on what you think. Your experiences aren't indicative of what other people are capable of.
This is something you already know. You're just trying to be difficult and prove your worth on this board. People who are reading these exchanges without bias can clearly see that. Certain things you say, like the last one I quoted, sound silly.