Life for transgender people is not easy, and even harder than what we thought. Whether it's a tranny date or life, it's tough for them. Lots of factors contribute to the extraordinarily high rate of suicide among transgender people, and misgendering is definitely one of them.
According to the 2014 National Transgender Discrimination Survey, 4.6% of the US population reported that they have attempted suicide at some points in their life, while that number was about 41% for transgender people. However, studies show that having a supportive family, like people who don't misgender can greatly reduce that rate. The 2015 US Transgender Study found that the rate of suicide attempts for BBW trans people with less supportive family was 54%, while it was 37% for those with supportive families. Misgendering contributes to a culture where violence against trans people is terrifyingly prevalent. A 2013 study by National Coalition of Anti-Violence Programs found that trans hookup people, and particularly trans women of color, were murdered at much higher rates than other LGBT people. Misgendering may not cause someone to go out and murder a trans person, but it does contribute to a culture in which hating disrespecting trans people is the norm, which does allow some people to justify violence against trans people. However you look at it, misgendering trans people cause real harm, and that applies to all trans people, not just ones you like, because there are some not so great trans people in this world, just as there are some not so great cis people, but everybody deserves to be gendered according to how they identify. If you misgender someone just because you disagree with them, you are basically telling all trans people around you that their humanity is conditional , and that the second you don't agree with them, their identity goes back to being invalid.
There are so many ways you can insult someone without disrespect all transgender and crossdresser. I know that sometimes you'll misgender someone unintentionally, maybe you didn't know their pronouns or you just made a mistake. Just correct yourself, move on, and try not do it again. You don't need to apologize profusely and make a huge deal out of it, that's probably drawing more unwanted attention to the situation anyway. But once you know someone's gender, if you continue to misgender them, that's when you get into violent territory. It can be tricky to switch over to new pronouns or a new name for someone, but if you respect them or trans people at all, you need to do it. All of this includes non-binary people. If someone ask you to use they/them pronouns, just do it. You should know that misgemdering a non-binary person is just as harmful as misgendering a binary trans person, non-binary identities are valid as well. So, intentionally misgendering trans people contributes to physical harm.
Trans people are the same as all of us, we need to accept them and respect them, so the first step is to respect who they are, respect their gender. Intentionally misgendering is an act of violence.