A very well worded and straight forward topic starter 😃 my compliments 😃
Many individuals here (including myself) enjoy rectal insertion due to the wealth of nerve endings concentrated there. Not letting a partner touch or go near your tender rosebud is 'your' choice and no one else's...no means no, simple as that, they must respect that, if not, then they are not interested in your needs. Setting and maintaining your boundaries until when or if you are ready is good.
Rectal stimulation/penetration can be very fun and lead to a very enjoyable orgasm if done on the recipient’s terms and not another individuals, it is your body, not theirs. Starting this thread is an excellent way to answer your curiosity regarding the positives & negatives about anal sex. Curiosity about additional aspects of ones sexuality is a good method of improving overall individual sexuality.
Taking into account that some individuals enjoy pain and such is not the case with you, it is quite understandable not liking the feel of something that caused you pain.
Many years ago when I first began to explore anal/rectal stimulation of my own sexuality, I did so at first by myself/solo so as to have complete control over what was pleasurable and not pleasurable for me. I started out with a diameter size that was much...much smaller than what normally passed, being that I instinctively did not want pain in my hiney. I then learned that relaxation, both mental & physical (being that they both work together) was essential if I was going to insert anything or enjoy it for that matter. Along with that, I quickly learned that thorough lubrication of not only the inserted object but also of the inside of my rectum 'is' essential, if not, the sensitive tissue inside becomes sore & irritated very quick, which translated into being painful & hurting which I did not like; it helped at the time that I already enjoyed enemas. I did not immediately make the connection though and I puzzled over the distasteful aspect of anything I inserted coming back out with unpleasant brown matter on it. A few episodes of that nature was all that it took for me to do what is today my favorite, gentle, slow clean out enemas, then presto... I was only left with mere flecks, if that, to wash & clean off the object. After that beginning, I, over time, ventured on to trial & error experimentation to find what was most satisfactory and comfortable for me. I would cast aside one thing or method or another and not go back, if I did, it was I had determined that at the time, I was too tense and gave it another attempt or tried it another way. I did this solo being that for me, I wanted to find out for myself what worked and what didn't, being that I am the one who knows best what my body is telling me in that regard, not some one else. I avidly read any and all "factual" information I could on the topic, quite often going to a local medical library(pre internet days) to read about the proper techniques for insertion into a patients rectum without harm and pain. I eventually got to the point where I was adept enough and relaxed enough that I progressed at a pace that was right for me from things the size of a thermometer, my finger (with glove or finger cot), or a nozzle to the present size that is just a bit smaller than what normally passes out with comfort. Having learned and addressed the concern of other undesired material coming out, and learning what the right amount of lubrication was for me, I then started over a length of time to gently stroke things in & out without distracting disturbances. By doing this whenever I chose or not, I eventually learned that if I was emotionally stressed or tense in any form, my rectal/anal sphincter just would not relax enough for any type of play in this fashion. I tried a few times and really didn’t enjoy the experience, so, in keeping with what my body was telling me, I did not/ do not force it...ever...no matter what. I would rather do without than have a bad experience. As to the potential risk of long term harm to myself, a guideline I use is what my body is telling me, I never insert anything myself or allow a lady friend to insert anything that is too large...period. Always keeping anything inserted a bit smaller than the maximum diameter that my sphincter will expand to, thereby preserving the normal muscle elasticity and having normal control without concern of leakage.
There was one exception, a lady who I had known for 5+ years and I decided to live together, we complimented each other sexually in all aspects including the current topic. One night we were pleasuring each other anally, I was deep in the throes of arousal about ready to climax when she abruptly became extremely rough with her insertions and it was painful, I used the safe word repeatedly and she would not stop. I immediately grabbed her hand and pulled it away along with the dildo, I then got up fully naked and removed her from my home, terminating the relationship then and there...that was 19 years ago...as mentioned before, no means no, it took a while for me to process that emotionally, accepting that one aberration with one individual in at the time, over 21 years did not substantiate my labeling the activity as entirely negative. There have been individuals since then with no negative experiences.
The point I am making an effort to communicate is that I view anal/rectal penetration as a very intimate activity, to be done gently & with all tenderness possible; otherwise it is not an option. It is an activity in which I am totally open to the other individual. That individual needs to know that for me, it requires tender gentleness and respect, just as I do with her. To do or view otherwise is a deal breaker, we may continue with some other sexual activity, but no anal/rectal penetration, that, at times, does result in our doing nothing and going separate ways, I would rather that outcome than have a negative experience. I hope that you might find something of benefit in my humble rambling, if not, that is all right too. If you have any questions, feel free to ask.