I don't see it as a bad thing to sleep in on the weekends since on the weekdays you're likely not getting the required amount of sleep that you truly need because of getting up early for work or school or staying up late to study etc.
I find I'm in a much better mood and more alert if I sleep in longer on the weekends when I don't have to set my alarm clock to go to work in the morning.
I feel more rested and ready for the day even though it's later in the day when I get up.
So sleep in on the weekends if you want too as long as you go to bed at the same time on the weekdays and wake up at the same time on the weekdays as well.
But by all means if you want to stay in bed for awhile longer on the weekends and it makes you feel better when doing so then go right ahead as it will do you no harm sleeping in.