A cringeworthy comment about waiting for Hilary Duff and the Olsen twins to turn 18. An inappropriate bet about tongue-kissing an underage co-star while filming.

Ashton Kutcher isn't the only entertainer to have made jokes of this ilk back in the early 2000s; however, the actor's past comments have resurfaced in light of the conviction of his longtime friend and former "That 70s Show" co-star Danny Masterson, who was sentenced Thursday to 30 years to life in prison for raping two women. Kutcher and his wife, Mila Kunis, who also starred on "That 70s Show," both wrote and later apologized for character letters in which they described Masterson positively.

To put it simply, Kutcher hasn't been accused of anything, and there is no reason to believe he is anything like Masterson. So why are Kutcher's past interviews being dissected by people all over the internet? Sociology and mental health experts say it's because friendship bonds are powerful − and people care deeply about who others choose to be friends with.

"There's a lot of research that shows how contagious our friends are," Shasta Nelson, friendship expert and author of "Frientimacy: How to Deepen Friendships for Lifelong Health and Happiness," says. "Our friends have the chance to shape our opinions, our preferences … our spiritual health, our physical health."

What our friendships say about us

Our friendships have a profound impact on our lives. They affect our immune system, longevity, mental health and overall happiness.

Though someone's friends don't reflect the totality of who they are, the general perception tends to be that someone's friends can clue you in on certain aspects their identity, Erica Chito Childs, a professor of sociology at Hunter College and The Graduate Center, CUNY, says.

"If you're spending time with people and you're choosing to spend time with them, it means that there's some level of commonality, and you are also at least in some way associated with their behavior."

More:Ashton Kutcher faces backlash for clips discussing underage Hilary Duff, Olsen twins, Mila Kunis

We also tend to have blind spots for our friends' bad behavior or when they fall short.

"When we like somebody, we tend to overlook or dismiss their problematic behaviors," Chito Childs says. "People sometimes can be very clear on seeing the flaws of those whom they don't know, but (with) their friends and their family, they explain it away."

More:Ashton Kutcher, Mila Kunis address 'pain' caused by Danny Masterson letters: 'We support victims'

What to do if a friend does something unequivocally wrong

So what happens when a friend does something unthinkable − like get convicted of a heinous crime?

It's a complicated experience and one that can raise deep feelings of betrayal and grief.

"It's also common for us to start questioning our own ability to choose people and our own judgments, and so it's very disorienting," Nelson says. "It's very destabilizing for people to go through these experiences."

More:'That '70s Show' actor Danny Masterson sentenced to 30 years to life in prison for 2 rapes

Psychotherapist Stephanie Sarkis says an important thing to keep in mind is that two things can be true at once − someone could have been a great friend to you and still have done horrible things to someone else.

"You can have a friend that is very nice to you, but also victimizes other people," Sarkis says. "That terrifies us as people, that there can be someone that is good to their kids, is a good employee, is a good friend of ours, and then they can have this entirely different side that we knew nothing about."

Experts offer the following guidance if you are in a situation where a close friend has done something horrifying:

• Respect the victims: "Think about how would you react if you were friends with the person who was on the other side of this, who was the one victimized," Chito Childs says. "Obviously it's difficult, but you have to try to also make sure that you yourself are not inflicting more harm."
• Feel your feelings: This can be done through therapy or journaling, Nelson says, encouraging people to ask themselves: "What fears does it bring up? What insecurities, what anger, what are the things I need to do to keep myself healthy? What do I need?"
• Reflect on if you still want to be friends: This is something that can also be good to do even with friends who haven't done anything bad, Sarkis says. "It's important just from time to time to do emotional inventory of our friendships," she says. "Look at what are the feelings you had the last time you met with a person. Do you feel supported? Do you feel respected? Are you afforded dignity in the relationship?"

More:Danny Masterson found guilty of 2 counts of rape in retrial, faces up to 30 years in prison