I identify with gentle parenting and actually I don't think it's difficult, I think it's the most natural and easiest way to parent. However, you have to have overcome certain messages/beliefs/patterns from your own childhood and you have to have the emotional maturity to sit with your child's emotions and to not be reactive - that's the most difficult part.
Eg gentle parenting
Child "I want an ice-cream"
Adult "We're not having an ice-cream right now because it's nearly lunchtime"
Child's emotional response which may include tantrum (usually related to factors like tiredness, hunger etc not whether they are "good" or "bad")
Adult does not relent and buy an ice-cream but neither do they scream at or punish the child for a completely normal emotional response. They help the child to identify the emotions, offer them empathy and try to redirect attention positively. They do not lose control. This is clearly not permissive aka "lazy" parenting.
I find the idea that gentle parenting is actually lazy/lax parenting interesting as in my experience self identifying gentle parents are parenting very consciously and are often (too) perfectionist. Gentle parenting is a type of authoritative parenting - it's not permissive parenting.
Often re "badly behaving" children whilst there may be aspects of permissive parenting I think the bigger factor is straightforward rolemodelling. If you demonstrate to children that when you have power over them you will exercise that power arbitrarily to do what you want without considering their needs/wants, then they will adopt a similar position towards you and others if they find that they are in the position of power. If you resolve conflict with your children by shouting, they will learn to resolve conflict by shouting. Etc Children who aren't considerate toward others are typically copying their parents who aren't considerate to others or them.
In these cases becoming (even) more authoritarian (which is different than authoritative) will work to suppress unwanted behaviour through fear, leading to the belief that "lax parenting" is the problem. But imo a better alternative is to teach children empathy and respect by showing them empathy and respect (!), which authoritarian parenting does not. It's completely possible to show children empathy and respect whilst remaining in control and giving them the security of boundaries and clear expectations.
Those who decide it's "gentle parenting" that's the issue when they see permissive parenting are unlikely to have asked the parents if they are "gentle parenting" so I kind of suspect they're just blaming gentle parenting based on their own misconceptions of what it is. Positioning authoritarian parenting as the only alternative to permissive parenting is obviously something that an authoritarian is likely to do. It doesn't make it true.